BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Kit Gallagher (QMUL) DTSTART:20200228T050000Z DTEND:20200228T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/1 DESCRIPTION:Title: Viable Gauge Choices in Cosmologies with Non-Linear Structur es\nby Kit Gallagher (QMUL) as part of Cosmology Talks\n\n\nAbstract\n Link to Video \n \nReference for cosmological perturbation theory: arxiv.org/abs/0809.4944\n\nReference for Post Newton ian Theory: Gravity\, by Eric Poisson\, Cambridge University Press\n\n
\n\nIndex to Key Parts of the Talk:\n\n0:00:00 Shaun's introduction\n\n0:01:05 < a href="https://youtu.be/ZqY54LXC4AQ?t=65">Kit's opening comments on the p aper: compared the differences in the gauge problems in two different approaches to approximating solutions to the Einstein field equations\; co smological perturbation theory (applicable on large scales)\; post-Newtoni an gravity (applicable on small scales)\; what the gauge problem is\; pape r/book references\;\n\n0:09:12 Q&A: Next steps: Issue on large scales - next gen galaxy surveys wil l require more realistic theoretical modeling than has been done in the pa st\; discussion of different approaches\; important precautions\n\n0:15:51 Why the paper's approach was not used before: using post-Newtonian ideas in cosmology is kind of a new thing to do\n\n0:16:29 T wo takeaways from the talk\n\n0:17:37 1st slide: Cosmological Perturbation Theory\n\n0:18:56 < a href="https://youtu.be/ZqY54LXC4AQ?t=1136">Conceptual problems: disc ussion leading to explanation of the gauge problem in cosmological perturb ation theory\n\n0:27:11 Post -Newtonian gravity: capable of dealing with large density contrasts\, provided...\n\n0:28:16 : the conditions under which a post-Newtonian expansion can be done\; 3 conditi ons\n\n0:31:40 Small vel ocities and weak field lead to...: mathematical consequences\; small t ime derivatives: equations change structure from wave equations to Poisson equations\n\n0:40:55 The ex plicit structure of all the gauge transformations\n\n0:49:17 Section IV A in paper: Spatially Flat Gauge choice\n\n0:52:13 Section IV B in paper: Synchronous Gauge choice\n\n0:52:42 Section IV F in paper: N-body Gauge ch oice\n\n0:53:13 Section IV G in paper: Longitudinal Gauge choice: important one to look at\n\n 0:57:40 Q&A on the N-body ga uge\n\n1:00:00 Section V of paper: Newtonian Motion Gauge\n\n1:04:40 Discussion on equation 89 in paper\n\n1:07:50 Applicability\n\n1:10:32 Summary\n\n1:16:17 Q&A: what are two simple things you 'd want viewers to take away from this talk?\n\n1:17:45 Q&A: outside of your own research\, what d o you think is the most interesting thing in cosmology at the moment?\ n\nReference for cosmological perturbation theory: https://arxiv.org/abs/0 809.4944\n\nReference for Post Newtonian Theory: https://www.cambridge.org /core/books/gravity/1F0CF38A59B1E51A63C7C3138268BE5D\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Seshadri Nadathur (ICG Institute of Cosmology and Gravitation\, Un iversity of Portsmouth) DTSTART:20200319T050000Z DTEND:20200319T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/2 DESCRIPTION:Title: Voids are powerful\, free and have tantalising insights on H 0\nby Seshadri Nadathur (ICG Institute of Cosmology and Gravitation\, University of Portsmouth) as part of Cosmology Talks\n\n\nAbstract\nSesh t ells us how the void-galaxy cross correlation provides information about c osmology via redshift space distortions and (importantly) the Alcock Paczy nski effect. The information is independent of Baryon Acoustic Oscillation s (BAO) and improves error bars by up to a factor of four. The combination of voids and BAO have very interesting insights into the Hubble discrepan cy and the late-time acceleration of the Universe.\n\nLink to video of tal k: youtube.com/watch ?v=UivvhqEuVuo\n\nThe most relevant papers for this talk: arxiv.org/abs/2001.11044 and arxiv.org/abs/1904.01030\n\n
\n\n< b>Index to Key Parts of the Talk:\n\n00:00 Shaun's introduction\n\n00:38 Sesh's opening comments on the paper: BAO and RSD have been studied for decades and applied to basically every spectroscopic galaxy survey but the void-galaxy cross-correlation measurement is someth ing that's pretty new\n\n01:40 Q&A: what are two simple things you'd want viewers to remember about thi s talk?: what a void-galaxy cross-correlation is and why it tells us a nything about cosmology\; the distribution of galaxies around the center o f low density void regions is anisotropic\, not symmetric\; details of tha t anisotropy\; usefulness as another method to measure the current expansi on rate of the universe\, H0\n\n04:18 Q&A: what was the motivation for this work?: interest in what can be done with voids\; by using the void-galaxy cross-correlation\, imp rovement can be made in the measurement precision of important quantities like the expansion rate and growth structure of the universe\; can improve the precision of such quantities by about a factor of two (equivalent to an increase in the survey volume without requiring any new data or observa tion time)\n\n08:13 First sli de: Void-galaxy basics: the distribution of galaxies around void locat ions\; anisotropic in redshift space\; not looking at void size but at dis tortion away from sphericity\, plot showing distortion due to galaxy veloc ities around voids (key segment 11:32 to 13:59)\; second and more interest ing and important effect (13:59 to 17:00)\n\n17:05 Correlations in redshift space: 2 sources of an isotropy - RSD (peculiar velocities\, growth rate) and Alcock-Paczynski ef fect\; why the void-galaxy correlation is a better measurement method than the standard auto-correlation technique\n\n19:57 Breaking the RSD/AP degeneracy: the quadrupole m oment of the void-galaxy correlation function\; Fig. 3 in paper \n\n25:33 Measuring ξvg in surveys\, 1st slide: various complications that have to be considered but left f or a different talk\n\n25:54 Measuring ξvg in surveys\, 2nd slide: simulations testing\; Fig. 7 a nd 8 (triangle plot showing posterior constraints on parameters of the joi nt RSD-AP model for the void-galaxy cross-correlation) in paper\; the impo rtant parameters in Fig. 8 are the AP parameter and the growth rate\, they are not strongly degenerate with each other\; were able to get a 1% measu rement of the AP parameter\n\n28:27 Cosmological implications I: Factor 2x improvement in precisio n (compared to BAO + FS\, full shape of the galaxy power spectrum)\; covar iance matrix\; about a factor of 4 improvement in Fap\; information that i s not available from usual 2-pt or 3-pt statistics\n\n32:35 Comparing voids to bispectrum: higher order statistics than just the galaxy power spectrum gives more informati on\; left panel shows same BOSS data but going from power spectrum to bisp ectrum\; right panel shows going from power spectrum to power spectrum + v oids\; the gain from adding voids far exceeds that from the bispectrum\n\n 35:32 Cosmological implicati ons II: direct evidence of acceleration independent of CMB and SN Ia ( picked up again at 43:15)\n\n34:47 Cosmological implications III: results from using combinations of BAO\, voids\, and Ly-a to determine H0 \n\n43:15 Back to Cosmological implications II: > 10σ e vidence of late-time acceleration (>> SN Ia)\; also direct evidence for DE \n\n47:39 the DE EoS can be constrained better with voids included and is consistent with a cosmologic al constant: Fig. 15 and discussion in paper\n\n48:07 Recap of the take-away messages: very p owerful method for analyzing data from galaxy surveys\, and it's essential ly for free as don't need any new observations and it tightens cosmologica l constraints\; some tantalizing answers on H0 discrepancy\; the strongest late-time evidence for DE comes from BAO+voids and not supernovae\n\n50:0 7 Q&A: outside of your own r esearch\, what do you think is the most interesting thing in cosmology at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Graham White (TRIUMF) DTSTART:20200326T050000Z DTEND:20200326T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/3 DESCRIPTION:Title: Light dark matter is an ideal mix of particle and cosmology< /a>\nby Graham White (TRIUMF) as part of Cosmology Talks\n\n\nAbstract\nGr aham tells us how Big Bang Nucleosynthesis (BBN) and the Cosmic Microwave Background can be used to constrain the potential existence of particles b eyond the Standard Model. \n\nThe focus is on light dark matter (masses le ss than 1GeV)\, which escapes direct detection bounds by being too light t o kick nucleons hard enough and is most interesting to cosmology because i t has precisely the masses relevant in the early universe processes we can "observe"\, e.g. BBN.\n\nGraham volunteered to give this talk on less tha n 36 hours notice\, so huge thanks to him for pulling something together s o quickly!!\n\nTalk video: youtube.com/watch?v=85sXsaj02yE\n\nGraham's paper: Cosmological Bounds on sub-GeV Dark Vector Bosons from Electromagnetic Energy Injection\n\n
\n\nIndex to Ke y Parts of the Talk:\n\n00:00 Shaun's introduction\n\n00:43 Graham's opening comments \n\n01:20 Q&A: what are two simple things you'd want viewers to re member about this talk?\n\n02:49 Q&A: What is the motivation for this work?: focus is on the ma ss range between 1 MeV and 1 GeV\, a particularly interesting region for c osmological constraints \n\n08:36 1st slide: Where to look for hidden sectors\n\n09:44 Why bother with cosmology?: tie-in with constraints previously identified\n\n10:51 Big Bang nucleosynthesis: 3 slides\n\n14:08 Electromagnetic Cascade: several processes outlined\; one very important thing that has been a little negl ected is final-state radiation\n\n15:22 Photon spectrum: 2 slides\; conventional wisdom is to use t he universal spectrum method\, but it breaks down in this sub-GeV case for several reasons\, see top of pg3 of paper\n\n16:09 the universal spectrum method results in orders of magnitude differences from the exact calculations at this scale: it wa s previously known this can occur near or below the GeV scale\n\n17:30 Light element abundances: 3 observables trying to constrain\n\n18:53 Boltzmann equations\n\n19:46 Nucleon-destruction\n\n20:42 Benchmarks for photon injection\n\n23:38 < a href="https://youtu.be/85sXsaj02yE?t=1418">Benchmarks for electron injec tion\n\n24:28 Monochroma tic injection: Figure 7 in paper\n\n26:08 Other model independent constraints: 2 slides\; Fig. 2 in paper\n\n28:01 Model d ependent constraints: 4 slides\; Figs. 1 and 3 in paper\n\n31:51 Discussion on the Lithium problem \n\n34:10 CMB ionization constraints: 3 slides\n\n38:05 CMB spectral distortion constraints: 2 slides\n\n38:57 COBE and PIXIE Limits: Fig. 5 i n paper\n\n39:23 Freeze in a bundances: 2 slides\; section 5.1 of paper\n\n42:04 Parameter constraints: Fig. 6 in paper\n\n 45:25 Conclusions\n\n46: 00 Q&A: Next steps\n\n49 :15 Q&A: Recap of take-away messages\n\n49:55 Q&A: o utside of your own research\, what do you think is the most interesting th ing in cosmology at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/3/ END:VEVENT BEGIN:VEVENT SUMMARY:Julien Lesgourgues (Institut für Theoretische Teilchenphysik und Kosmologie\, RWTH Aachen University) DTSTART:20200402T050000Z DTEND:20200402T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/4 DESCRIPTION:Title: Cosmology won't measure individual neutrino mass states\ nby Julien Lesgourgues (Institut für Theoretische Teilchenphysik und Kosm ologie\, RWTH Aachen University) as part of Cosmology Talks\n\n\nAbstract\ nJulien tells us about the cosmological effects of different neutrino mass states (i.e. the same sum of masses\, but different masses for each indiv idual neutrino - e.g. "normal" vs "inverted"). \n\nThere are effects\, but they're all very small and not even the best future experiments will dist inguish them.\n\nNon-standard model neutrinos would still have interesting effects\, but it seems that cosmology's insight on the SM ones will be li mited to the sum of the masses.\n\nVideo of talk\n\nPaper: [2003.03354] What will it take to measure individual neutrino mass states using cosmology?\, by Maria Archidiacono\, Steen Hannestad \, Julien Lesgourgues\n\nSupplemental info: Review of paper by Sunny Vagnozzi\n\n
\n\nIndex to Key Parts of the Talk:\n\n[00:01] Shaun's intro to the topic and Julien's wo rk\n\n[00:32] Julien's ope ning comments summarizing the paper's findings \n\n[01:46] Q&A: what are two simple things you'd wa nt viewers to remember about this talk?: two take-home messages\, one for particle physicists and one for cosmologists\n\n[04:01] Q&A: what is the motivation for this work?< /a>: there were many papers addressing the same question but situation not crystal clear\, this work used Bayesian evidence which was not used befor e and also discusses in detail the physical effects of different mass spli ttings on the cosmological observables\n\n[05:21] Title page from the paper and collaborators\; definit ions of acronyms and proxies that will be referred to: normal (NH)\, i nverted (IH)\, and degenerate (DH) hierarchy\; Proxy 1 (1 massive + 2 mass less)\, Proxy 2 (2 massive + 1 massless)\n\n[08:09] Plot of total neutrino mass vs lightest\, commentar y on Fig. 1 of paper\n\n[11:23] Total background density evolution for IH and NH compared to the eq uivalent DH model\, Fig. 2b from paper\n\n[15:11] CDM density perturbation evolution for IH or NH c ompared to the equivalent DH model\, Fig. 4a\n\n[17:06] The power spectrum of the different models \; Fig. 5 from paper \n\n[20:54] Observable galaxy power spectrum\, Fig. 7a: probably the most interesting plot\, reformulated in terms not of the theoretical matter po wer spectrum but of the real observable power spectrum that Euclid will me asure\; all done analytically or semi-analytically with CLASS code and sta rting from linear observables\n\n[25:45] Observable weak lensing\, Fig. 7b\n\n[26:13] Ratio of the lensed angular power spectr a of temperature\, E-mode polarization\, and B-mode polarization for the s ame models\, Fig. 6b\n\n[28:54] Mass reconstruction forecast using DH instead of fiducial NH/IH + Bayesian evidence ratio of "correct" / DH\; Fig. 8\n\n[32:04] Julien's recap comments on the paper 's findings\n\n[36:28] Q &A: Next steps\n\n[39:05] Q&A: outside of your own research\, what do you think is the most intere sting thing in cosmology at the moment?\n\n[41:35] Q&A on spatial curvature\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Deanna C. Hooper (University of Brussels) DTSTART:20200409T060000Z DTEND:20200409T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/5 DESCRIPTION:Title: CMB spectral distortions are a prime untapped resource\n by Deanna C. Hooper (University of Brussels) as part of Cosmology Talks\n\ n\nAbstract\nDeanna tells us about what we could learn from future measure ments of the spectral distortions in the CMB\, as well as how spectral dis tortions complement current and future measurements of CMB anisotropies. S he also discusses CLASS (v3.0)\, the code you can (very soon) use to calcu late predictions for both.\n\nThere is a guaranteed spectral distortion si gnal to detect within ΛCDM and the possibility to constrain many possible deviations\, including primordial black holes and decaying dark matter. I n fact\, we can detect the signal even if the PBHs and/or decaying dark ma tter only make up one part in a million of the total dark matter!\n\nWhy h ave we waited so long (and are still waiting) for an updated measurement a fter COBE-FIRAS\, which is now more than 25 years old?! I don't know\, but hopefully it won't be another 25.\n\nVideo of Talk\n\nPaper: [1910.04619] The synergy between CMB spectral distortions a nd anisotropies\, by Matteo Lucca\, Nils Schöneberg\, Deanna C. Hoope r\, Julien Lesgourgues\, Jens Chluba\n\nCLASS\, the Cosmic Linear Anisotropy Solving Sy stem\n\nSupplemental Info: \n\nDeanna's 20-tweet thread on this paper\n\ nDeanna also does live streams about cosmology/the universe on Periscope. These are aimed at a general audience: https://www.pscp.tv/DCHooper91/1LyxBNjVbzjxN\n\n\n\nIndex to Key Parts of the Talk:\n\n[00:02] Shaun's intro to the topic and Deanna's work\ n\n[00:45] Deanna's opening co mments on this work: spectral distortions (SDs)\, deviations from a pe rfect black body spectrum\, have very much not been exploited to full pote ntial\; a whole new region of parameter space can be explored\; first step was to implement the full calculation of SDs in the standard Boltzmann co de CLASS\; can now produce both the anisotropy and SD predictions for the same model\n\n[01:52] Q&A: wh at are two simple things you'd want viewers to remember about this talk?: (1) SDs are the future of CMB\, even with future CMB missions\; SDs wi ll allow several orders of magnitude improvements in some regions of param eter space\, and (2) we now have a very powerful tool in CLASS v3 which co mputes SDs in parallel with anisotropies.\n\n[02:33] Q&A: what is the motivation for this work?: th ere is only one observation of the spectrum of CMB photons from COBE-FIRAS 25-years ago\, with deviations of 10^-5\; but even with ΛCDM\, SDs are c learly predicted on the order of 10^-8\; if an SD mission does not measure anisotropies at 10^-8\, it means ΛCDM is wrong\; other models also predi cting SDs\; an SD mission could distinguish between models\; observation i s really lagging behind the theory\; SDs are extremely well understood\, s tudied for 30-40 years\; improvements in code\, mainly by Jens Chluba\; SD missions have been proposed but not yet funded\n\n[05:42] Q&A (an aside): Why is it taking so long for a new mission to probe SDs?: problem of foreground removal\; perhaps overlooked as only a small part of the community is pushing for this\; gai ning more and more attention now\; being able to test the predictions of ΛCDM is something we should be doing\; NASA roadmap includes SDs but noth ing officially approved yet\; feasible to have measurements within 15-20 y ears\n\n[07:20] Returning to motivations: paper is long but intended as a review of the whole forma lism which streamlines earlier literature and details of the new CLASS cod e\n\n[08:52] Slide of paper t itle page and collaborators\n\n[09:07] Main Technicalities of Spectral Distortions: 4 contribut ions to the total distortion to the photon intensity spectrum\; other comm ents on frequency bins\, amplitude of the SDs\, heating function\, branchi ng ratios\n\n[17:10] Branchi ng ratios slide: CLASS calculations plot of the 4 distortion types\n\n [21:42] SDs to the total pho ton intensity caused by ΛCDM processes and basic extensions: testable prediction of ΛCDM if we had the satellite to do it\n\n[24:20] SDs to the total photon intensity cau sed by DM decay and annihilation: Decaying DM can be constrained by SD s\; Fig. 1 left panel and Fig. 2 right panel in paper\n\n[25:40] Heating rate produced by DM decay and annihilation: Fig. 4 left panel in paper\n\n[26:20] SDs to the total photon intensity caused by P BH evaporation: Figure 5 right panel in paper.\n\n[27:10] Making mock data to see what we'd be abl e to do with future missions\n\n[28:26] Constraints from different current and future missions for ΛCDM + n_run: 5 different cases involving combinations of Planck\, F IRAS\, PIXIE\, LiteBIRD\, CMB-S4\, PRISM\; Fig. 7 in paper\n\n[33:10] Constraints on decaying DM fract ion as a function of the particle lifetime: Deanna's favorite plot fro m the paper\, Fig. 8\; the part of the plot where spectral distortions are needed\; different regions of parameter space\, one can be constrained by anisotropies and the other with SDs\n\n[35:55] Constraints on PBHs as a function of their mass: t hey found a new way to study PBH evaporation\; Fig. 9 in paper\n\n[39:05] Q&A about using CLASS v3 \n\n[40:19] Next Steps: 2 papers in the pipeline using this framework\; 3rd paper on foreground re moval\n\n[42:56] Reiterating 2 takeaway points from talk\n\n[43:40] Q&A: outside of your own research\, what do you think is t he most interesting thing in cosmology at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Omar Darwish (DAMP\, University of Cambridge) DTSTART:20200416T060000Z DTEND:20200416T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/6 DESCRIPTION:Title: Lensing maps are great\, but they're even better with the tS Z effect removed!\nby Omar Darwish (DAMP\, University of Cambridge) as part of Cosmology Talks\n\n\nAbstract\nOmar tells us about the excellent quality lensing map he's produced with the Atacama Cosmology Telescope col laboration. You honestly won't believe how well this lensing map correlate s with the cosmic infrared background (sorry about the clickbait). \n\nThi s map will be incredibly useful to cross-correlate with any dataset of tra cers inside the relatively large window of ACT observations. It will be pu blic very soon\, so once it is you should definitely be using it!\n\nOmar also explains how he and the collaboration\, for the first time\, removed the annoying thermal Sunyaev–Zeldovich contamination that ordinarily pro duces a ~10% bias in sigma8 (and thus any other cosmological parameter cor related with sigma8).\n\nVideo of Talk\n\nPaper: [2004.01139] The Atacama Cosmology Telescope: A CMB lensing mass map ove r 2100 square degrees of sky and its cross-correlation with BOSS-CMASS gal axies\n\nReview of paper by Sunny Vagnozzi\n\n
\n\nIndex to Key Pa rts of the Talk:\n\n[00:02] Shaun's introduction\n\n[00:23] Omar's opening comments on this work\n\n[02:24] Q&A: what are two simple things you'd want v iewers to remember about this talk?\n\n[05:32] Q&A: what is the motivation for this work?\n\n[0 7:52] Title slide of talk and collaborators: ACTPol lensing maps and foreground-cleaned galaxy corr elations\; with Mathew Madhavacheril\, Blake Sherwin\, and the ACT Collabo ration\n\n[08:45] CMB Lensing Intro: lensing deflection field\; lensing convergence field κ \n\n[1 2:02] CMB Lensing Reconstruct ion Basics\n\n[14:27] ACT Experiment: effective area BOSS-North + Deep56 ~ 2100 sq deg\; overla p with multiple surveys (BOSS\, DES\,...)\n\n[16:11] CMB Lensing from ACT: Deep56 ACTPol Lensing [16:31]\; Deep56 ACTPol Len sing vs Planck CIB [19:41] (plot shown here is top part of Fig. 2 in paper)\; BOSS-N ACTPol Lensin g vs Planck CIB [20:52] (bottom part of Fig. 2 in paper)\n\n[21:32] ACT CMB Lensing Maps\n\n[25:38] Many CMB Lensing x Galaxy papers\n\n[27:16] One particular systematic effe ct for low-z galaxy lensing cross correlations: this effect will becom e important for AdvACT and Simons Observatory\n\n[30:44] Systematics: tSZ contamination: important for TT dominated lensing maps\; negative bias ~10 - 20%\n\n[32:06] Removing tSZ contamination: th ree slides\n\n[36:07] tSZ cl eaned CMB lensing maps from ILC ACT+Planck\n\n[38:20] Symmetrising gradient cleaning for foregroun d removal\n\n[44:36] Min imum variance forecasted lensing noise\n\n[45:24] Contaminated vs non-contaminated measurement \n\n[46:07] Simple amplitude fit\; refers to Fig. 5\, pg10\, of paper\n\n[46:45] Next Steps\n\n[48:37] Conclusions\n\n[49:40] Q&A: outside of your own research\, what do you think is the most interesting thing in cosmology at the moment?\n\nSup plemental info: A tweet thread by Shaun about this talk\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Jurek Bauer (Georg August University of Göttingen) DTSTART:20200424T060000Z DTEND:20200424T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/7 DESCRIPTION:Title: Fuzzy dark matter arising from GUT scale physics should be r uled in/out by SKA\nby Jurek Bauer (Georg August University of Göttin gen) as part of Cosmology Talks\n\n\nAbstract\nJurek tells us about the pr ospects for constraining axion (aka ultralight aka fuzzy) dark matter with future 21cm intensity mapping survey such as SKA and HIRAX.\n\nAxion mode ls arising from specific energy scales predict that an axion with a given mass will only provide a certain fraction of the total dark matter. It see ms plausible that with SKA we will be able to detect ultralight dark matte r even if it arises from a GUT scale axion model. An observational noise m odel for SKA was included to make this claim\, but as of yet no theoretica l uncertainty is included in the calculation.\n\nVideo of talk\n\nPaper: [2003.09655] Intensity Mapping as a Probe of Axi on Dark Matter\, by Jurek B. Bauer\, David J. E. Marsh\, Renée Hlože k\, Hamsa Padmanabhan\, Alex Laguë\n\n
\n\nIndex to Key Parts of th e Talk:\n\n[00:02] Shaun's intro to the topic and Jurek's work\n\n[00:57] Jurek's brief summary of the paper: we investigat ed the impact of ultralight axions on 21cm intensity mapping (IM) in the p ost-reionization universe\; vastly increases the accessible modes\; use a data-driven framework for the HI power spectrum provided by the HI halo mo del of Padmanabhan+ 2017 (a separate Cosmology Talk is available on this a t youtu.be/K8bS_52_XMk)\; etc. \n\n[02:27] Q&A: what are two simple things you'd want viewers to remember about this talk?: (1) th eir HI halo model allowed extending the axion phenomenology to a completel y new level\; it highlights the importance of the bias\, and (2) exciting prospects with near future surveys (SKA1MID\, HIRAX\, CMB-SO)\, which in c ombination can test the theoretical predictions\n\n[03:54] Q&A: what is the motivation for this work?: ultralight axions (ULAs) are a well-motivated DM candidate\, and (2) w ork by Carucci+ 2017 (more at [29:02])\n\n[08:39] Fir st slide: What is 21cm Intensity Mapping?: includes commments on Fig. 13\, pg12\, of the paper\n\n[10:40] Axion Physics: large de Broglie wavelength introduces scale-dep endent pressure\; ULAs suppress the matter power spectrum on small scales\ , depending on their mass\; axionCAMB used for computation. See section 2. 1 and Fig. 1 of the paper.\n\n[12:57] Modeling the 21cm signal\; halo mass function (HMF)\; halo bi as\; neutral hydrogen - halo mass relation\; neutral hydrogen density prof ile\; redshift space distortions are ignored in the present study\, a cons ervative assumption (see pg4 of paper)\n\n[16:47] HI Halo Model: comments based on Fig. 2\, pg4\, of paper\n\n[17:52] Modeling the 21cm signal: Use spherical harmonics tomography: slice survey vol ume into redshift bins and do spherical harmonic decomposition for the sur face\, similar to CMB\n\n[19:30] Accommodating Axions: comments on Fig. 3 on pg6 of the paper\n\n[ 22:39] HMF and HI bias: comments on Figs. 4 and 5\, pg6\, of the paper\n\n[26:20] The HI Power Spectrum for the ULAs: comm ents on Fig. 6\, pg 7\, of the paper\n\n[29:02] Comparison to HI Power Spectrum simulation by Carucci+ 2017: similar trend but an offset\; comments on Fig. 7\, add'l detail s on pg8 of paper\n\n[32:26] Degeneracy Structure: 4 parameters are highly degenerate\; ways to br eak degeneracies\; Fig. 10 comments\, add'l details on pg11 of paper\n\n[3 4:44] Error on Axion Fractio n - Overview: comments on Fig. 9\, pg10\, of the paper\n\n[38:40] Combining IM with CMB-SO: co mments on Fig. 12\, pg12\, of the paper\n\n[39:28] SKA1MID and HIRAX surveys: exclusion limits\; c omments on Fig. 14\, pg13\, of the paper\n\n[44:08] Q&A: What's next?\n\n[44:58] Two takeaway comments\n\n[45:41] Q&A: outside of your own research\, what do you think is the most interesting thing in cosmology at the moment ?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/7/ END:VEVENT BEGIN:VEVENT SUMMARY:W. L. Kimmy Wu (KICP at the University of Chicago) DTSTART:20200501T060000Z DTEND:20200501T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/8 DESCRIPTION:Title: Planck lensing and line of sight BAO in mild tension. A vita l clue in the Hubble mystery?\nby W. L. Kimmy Wu (KICP at the Universi ty of Chicago) as part of Cosmology Talks\n\n\nAbstract\nKimmy tells us ab out a subtle but very interesting tension between Planck lensing data and line of sight Baryon Acoustic Oscillation (BAO) data.\n\nShe and her coaut hors discovered this via an intriguing mismatch between Planck and South P ole Telescope (SPT) lensing results. The Planck and SPT power spectrum amp litudes matched\, but when combined with BAO and Big Bang Nucleosynthesis the inferred Hubble parameters were slightly different.\n\nLike great data -detectives they tracked the source of this discrepancy down to the mismat ch between Planck lensing and line of sight BAO. Why the line of sight BAO might be causing this is unclear. On the Planck lensing side\, it has som ething to do with the shape of the lensing power spectrum\, e.g. the locat ion of the peak - because SPT only measures the power spectrum's tail and so is only sensitive to the amplitude.\n\nThe result is definitely interes ting\, and unknown by the community until now (as far as I'm aware). Wheth er it is a red herring or a vital clue in the hunt to solve the Hubble mys tery remains to be seen. But it should provide fuel for both model builder s and hunters of systematic errors trying to solve this mystery.\n\nVideo of talk\n\nPaper : [2004.10207] Hubble constant tension between CMB lensing and BAO measurements\, by W.L. Kimmy Wu\, Pavel Motloch\, Wayne Hu\, Marco Raveri\n\n
\n\nIndex to Key Parts o f the Talk:\n\n[00:02] Shau n's intro to the topic and Kimmy's work\n\n[01:10] Kimmy's brief summary of the paper: A tension metric\, the update difference in mean parameters\, is applied to trace t he origin of the observed differences in H0 between Planck and SPT lensing measurements when both are combined with BAO measurements with a baryon d ensity prior\n\n[01:52] Q&A: what are two simple things you'd want viewers to remember about this talk? : (1) a surprise result\, the driver of the tension between the two da ta sets is a mild tension between the Planck lensing data set and BAO meas urements (in particular\, the line-of-sight BAO measurements appear to be an outlier)\, and (2) a very good use case for this update difference in m ean tension metric\, it allows the data to tell what are the interesting p arameter directions to look at\n\n[04:42] Q&A: what is the motivation for this work?: A little hist ory on how they stumbled across this curiosity\; first slide: Ωm\, H0 con straints with galaxy BAO + BBN prior\; SPTpol lensing and Planck lensing a re consistent\, but there is something about adding BAO and BBN that draws out various features of the lensing spectrum that causes a difference in the H0 inference \n\n[11:04] Brief overview of CMB lensing measurements\n\n[12:51] Planck and SPTpol lensing measurements\n \n[14:18] The BAO measurement s \n\n[15:37] Perpendicul ar and Parallel BAO\n\n[17:00] Tension metric: update difference in mean parameters\, Qudm: a modified version of the simpler metric\, difference in mean parameters\, w hich works well if both data sets are Gaussian\; Qudm is useful where A's posterior is Gaussian but B's is not\, but where A + B are sufficiently ap proximately Gaussian\; usefulness of KL decomposition (more details in the paper in section II: Quantifying Tensions)\n\n[22:51] Choosing the Parameter basis\n\n[26:35] Qudm: BAO + BBN + SPTpol lens u pdate with Planck lens: How much fractional constraining power each KL mode contributes to a parameter\n\n[30:17] Qudm: BAO + BBN update with Planck lens\n\n[32:59] Parallel and perpendicular BAO measurements are consistent\n\n[35:37] Parallel BAO contributes most to the mild tension between P lanck lensing and BAO+BBN\n\n[39:50] High best-fit Ωm to parallel BAO => high H0\n\n[40:53] < a href="https://youtu.be/JEFQqnxP2jk?t=2453">Redshift slope in parallel BA O measurements drives high Ωm\n\n[42:20] High Ωm strongly ruled out\n\n[44:23] Q&A: Where to next?\n\n[47:30] Q&A: What might be causing the Hub ble tension?\n\n[50:18] Q&A: outside of your own research\, what do you think is the most interest ing thing in cosmology at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Adam Riess (Johns Hopkins University) DTSTART:20200506T060000Z DTEND:20200506T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/9 DESCRIPTION:Title: Cepheid crowding is not the cause of the Hubble tension\ nby Adam Riess (Johns Hopkins University) as part of Cosmology Talks\n\n\n Abstract\nAdam tells us about what he and collaborators considered to be t he leading candidate for a systematic error in the SHOES measurement of th e expansion rate of the Universe. This is "Cepheid crowding"\, the possibi lity that background sources change our interpretation of Cepheid brightne ss\, ruining one step in the SHOES distance ladder.\n\nThey devise a nice way to test whether the crowding is correctly accounted for and find that it is. So crowding cannot be the "explanation" of an error in the distance ladder measurement of H0.\n\nHe also stresses that both the early and lat e universe measurements of H0 are now backed up by multiple different meas urements. Therefore\, if the resolution isn't fundamental physics\, then n o single systematic can entirely solve the tension.\n\nWe also discuss a f ew topics around the H0 tension\, including what resolution of the tension he would pick as most likely if forced to gamble (answer: a deviation fro m vanilla ΛCDM in the early universe)\n\nVideo of talk\n\nPaper: [2005.02445] The Accuracy of the Hubble Constant Measur ement Verified through Cepheid Amplitudes\, by Adam G. Riess\, Wenlong Yuan\, Stefano Casertano\, Lucas M. Macri\, Dan Scolnic\n\n
\n\nInd ex to Key Parts of the Talk:\n\n[00:02] Shaun's intro to the topic and Adam's work\n\n[00:57] Q&A: Adam's brief summary of the paper: Cepheid crowding can be ruled out at greater than 5σ as an iss ue causing the Hubble tension\n\n[02:58] Q&A: what are two simple things you'd want viewers to remember about this talk? \n\n[04:21] Q&A: what is the motivation for this work? Of all the potential syst ematics to check\, why is crowding the one that you chose?\n\n[06:09] First slide: the paper and th e SH0ES colleagues involved\n\n[06:49] Background on the Hubble tension problem\n\n[08:38] The distance ladder method for me asuring the Hubble constant: late universe method\n\n[09:31] Representative early universe methods to determine the Hubble constant: early vs late universe determinatio ns differ by 5-6σ (*see Adam's later comment at [37:23] on his rule of th umb to clarify what differentiates early vs late universe methods)\n\n[10: 54] Why do we use Cepheid var iable stars?: includes brief comments on other calibration methods bes ides Cepheids\n\n[12:38] Impo rtance of Cepheids since there aren't enough supernovae to build the dista nce ladder just from SNe\n\n[13:14] Cepheids and Crowding - the non-trivial challenge: idealize d situation vs reality for accurate photometric measurements\; cannot reso lve the non-uniform background under Cepheids but that must be accounted f or to measure accurate photometry\; image showing what crowding is\; how t o figure out how much crowding there is\; measuring the offset or bias tha t results on average from the other field stars that are crowding into the resolution element\; extra wrinkles\; possibly the most significant chall enge for Cepheid measurements beyond 20 Mpc is crowding and blending from redder stars particularly in near-infrared observations (Wendy Freedman qu ote)\n\n[15:44] Amplitudes Pr ovide Direct Measure of Cepheid Crowding: crowded flux is bigge r fractional contribution when Cepheid at minimum\, which compresses the l ight curve amplitude\; mathematical relationship\n\n[18:09] Three Examples of Different Crowding Level s: NGC 1559: illustrates the amplitude compression effect from crowdin g\n\n[19:45] Step 1: Calibra te Amplitude-period Relation with Milky Way Cepheids: Cepheid amplitud es depend on period\; expected amplitude as a function of period and crowd ing\n\n[21:01] Step 2: 224 N IR amplitudes Measured in 4 hosts\, compare to Milky Way (benchmark): empirically measured amplitudes match prediction (with no free parameters) from crowding assessed in the conventional way from local (Milky Way) reg ions\, confirming their accuracy for estimating the background at the (ext ragalactic) Cepheid locations\n\n[23:21] Step 3: Constrain "unrecognized" crowding\, compare to Hubble tension: "unrecognized" crowding needed to explain Hubble tension rul ed out at >5σ\n\n[25:10] So what could explain the Hubble tension?\n\n[32:56] Future Prospects: Improvements coming in the ne xt couple years\n\n[34:50] Q&A: If you had to guess right now\, what is the most probable explanat ion on either the theory or observational side?\n\n[37:23] *Adam's rule of thumb to clarify what d ifferentiates late universe vs early universe methods\n\n[39:13] Q&A: could a breakdown in the FRW metric at late times be an explanation?\n\n[41:10] Q&A: outside of your own research\, what do yo u think is the most interesting thing in cosmology at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/9/ END:VEVENT BEGIN:VEVENT SUMMARY:J. Colin Hill (Columbia University) DTSTART:20200515T060000Z DTEND:20200515T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/10 DESCRIPTION:Title: Early dark energy doesn't make cosmology concordant again\nby J. Colin Hill (Columbia University) as part of Cosmology Talks\n\n\ nAbstract\nColin tells us about how even though early dark energy can alle viate the Hubble tension\, it does so at the expense of increasing other t ension. Early dark energy can raise the predicted expansion rate inferred from the cosmic microwave background (CMB)\, by changing the sound horizon at the last scattering surface. However\, the early dark energy also supp resses the growth of perturbations that are within the horizon while it is active. This mean that\, to fit the CMB\, the matter density must increas e (and the spectral index becomes more blue tilted). The consequence is th at the matter power spectrum should get bigger.\n\nIn their paper\, Colin and his coauthors show that this affects the weak lensing measurements by DES\, KiDS and HSC\, and therefore including those experiments in a full d ata analysis makes things discordant again. The Hubble parameter is pulled back down\, restoring most of the tension between local and CMB measureme nts of H0\, and the tension in S_8 gets magnified by the increased mismatc h in the predicted and measured matter power spectrum.\n\nIt is also worth noting that\, if you exclude the local measurements of H0\, there is no p reference for early dark energy in the data.\n\nThere is hope\, perhaps. I f the sound horizon could be changed without altering the growth of pertur bations that might still be a valid resolution\, but it is unlikely to be caused by early dark energy (alone).\n\nVideo of talk\n\nPa per: [2003.07355] Early Dark En ergy Does Not Restore Cosmological Concordance\, by J. Colin Hill\, Ev an McDonough\, Michael W. Toomey\, Stephon Alexander\n\nReview of paper by Sunny Vagnozzi\n\n
\n\nIndex to Key Parts of the Talk:\n\n[00:02] Shaun's intro to the topic and Colin's work\n\n[01:15] C olin's summary of the 2003.07355 paper\n\n[04:52] The broader context to Colin's motivation for thi s work\n\n[08:16] First s lide: The Hubble Constant\n\n[08:54] Early Dark Energy: earlier EDE papers\; summary plot\; the chain of reasoning leading to the EDE models with a reference to Knox and Millea for a nice review\, 190 8.03663\; EDE models decrease the physical size of the sound horizon i mprinted in the CMB - they have added flexibility due to a set of 3 additi onal new parameters that are relevant in the calculation of the physical s ize of the sound horizon\n\n[12:27] How the EDE model has been implemented from a more physical perspec tive: a new (pseudo)-scalar field important prior to recombination\, w hose energy density contribution decays away rapidly just before the redsh ift of last scattering\; the mass of the scalar field needs to be ~ 10 ^-2 7 eV\n\n[17:36] The actual p arameters used to describe this model: 3 physical parameters - mass of the field\, a decay constant\, and its initial position on the potential\ ; these are converted into phenomenological parameters which are more clos ely related to what the data can actually constrain\; plot showing fractio nal contribution of EDE to cosmic energy budget as function of z\n\n[20:05 ] EDE maintains a good fit t o CMB power spectrum data with higher H0: plot shows a sub-percent dif ference in the TT power spectrum between ΛCDM (H0=68.21) and EDE model (H 0=72.19)\n\n[21:40] What abo ut large-scale structure?: motivation for the project - no one had mad e a plot of the matter power spectrum P(k)\; modified version of the Boltz mann code\, CLASS_EDE\, is public on github\n\n[22:26] Plot of the matter power spectrum comparing ΛC DM and EDE models: the plot of their ratio highlights the significant differences\n\n[24:19] Param eter Shifts are the driver for these differences: caused by parameter shifts in the so-called normal cosmological parameters in the EDE scenario compared to ΛCDM\; also a noticeable shift in the scalar spectral index\ n\n[27:38] Interesting physi cal effects due to the EDE itself\n\n[30:28] Updated EDE Analysis Including Large-Scale Structure Data Sets: includes 2 data sets not included in previous work: DES "3x 2pt" full likelihood and S8 constraints from HSC and KiDS\; Cobaya code us ed for the MCMC sampling\n\n[33:08] Inclusion of LSS Data\n\n[35:07] Inclusion of DES/HSC/KiDS: inclusion of LSS data lead s to non-detection of EDE component\n\n[36:28] Analysis without SH0ES: comparing all data sets wit hout SHOES\; looking at the posteriors in the EDE parameter space\; broade ning of error bars when analyzing EDE model\, but no major shifts seen\; H 0 tension persists\; strong upper limit on existence of EDE component\; SH 0ES is in 3.5σ tension with other data sets (even in EDE model)\; bottom line: you can't shift the parameters in the way that's needed for the CMB without messing up the large-scale structure data\n\n[38:42] Summary: SHOES is the only data set d riving preference for EDE (moderate evidence\, ~ 2σ)\n\n[40:43] Physical Priors: uniform priors o n f_EDE and log(z_c) are very non-uniform on physical scalar field paramet ers f and m\n\n[41:34] Final Summary: \n\n\n[42:45] Q&A: Where to next?: upcoming release o f ACT cosmological parameter measurements in the next couple months\; the observables that dominate the constraining power are different between ACT (TE) and Planck (TT).\n\n[44:19] Q&A discussion on the sound horizon issue): to be consistent wit h LSS\, the sound horizon would need to be changed (lowered) in a way that does not then act to suppress the growth of pertubations\n\n[45:49] Q&A: what do you think is the mos t probable explanation of H0 tension?\n\n[48:13] Q&A: Outside of your own research\, what do you t hink is the most interesting thing in cosmology at the moment?\n\nOthe r Paper References:
\n[1811 .04083] Early Dark Energy Can Resolve The Hubble Tension\, by V. Pouli n\, T. Smith\, T. Karwal\, M. Kamionkowski
\n[1908.06995] Oscillating scalar fields and the Hubble ten sion: a resolution with novel signatures\, by T. Smith\, V. Poulin\, M . Amin
\n[1905.12618] Acoust ic Dark Energy: Potential Conversion of the Hubble Tension\, by M. Lin \, G. Benevento\, W. Hu\, M. Raveri
\n[1904.01016] Rock 'n' Roll Solutions to the Hubble Tension\, by P. Agrawal\, F. Cyr-Racine\, D. Pinner\, L. Randall\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/10/ END:VEVENT BEGIN:VEVENT SUMMARY:Hamsa Padmanabhan (CITA\, University of Toronto) DTSTART:20200529T060000Z DTEND:20200529T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/11 DESCRIPTION:Title: The overlap between HI halo modelling and cosmology\nby Hamsa Padmanabhan (CITA\, University of Toronto) as part of Cosmology Tal ks\n\n\nAbstract\nHamsa tells us about how baryonic gases arrange themselv es inside galaxies\, specifically in the context of the HI halo model (wit h some deviation to discuss other gases like molecular hydrogen and carbon monoxide).\n\nThis is a great talk in its own right\, full of really usef ul information for cosmologists who want to know how intensity mapping\, e tc\, will be used for cosmology - but\, it also acts as a good companion t alk to Jurek Bauer's talk on constraining axion dark matter using intensit y mapping (https://w ww.youtube.com/watch?v=bMlrDOWw978). Hamsa was a coauthor on Jurek's p aper and the expert in that collaboration on the HI/intensity mapping part .\n\nThis video builds up to eventually being about this paper\, https://arxiv.org/abs/2002.01489\, h owever in getting there it covers the whole background of modelling HI and other baryonic gases within galaxies in an information packed\, but acces sible way.\n\nVideo of talk\n\nPaper: [2002.014 89] New empirical constraints on the cosmological evolution of gas and sta rs in galaxies\, by Hamsa Padmanabhan\, Abraham Loeb\n\n
\n\nInd ex to Key Parts of the Talk:\n\n[00:01] Shaun's introduction to Hamsa's work\n\n[01:12] Hamsa's brief summary of the paper and her work\n\n[03:27] Q&A: what are two simple things you'd want viewers to remember about this talk? \n\n[06:22] Q&A: What pro blems were unsolved that motivated this work?\n\n[09:21] Details on the paper: "everything here is more or less centered around this innovative technique known as intens ity mapping...it's been gaining a lot of attention over the past few years and in fact over the last decade"\n\n[10:02] What intensity mapping is: "much faster and much chea per" than other methods\; "it can be done for different lines\, for differ ent tracers of large scale structure (e.g.\, 21cm\, CO\, C+)"\n \n[11:22] Impact of astrophys ics and the "astrophysical systematic" that needs to be quantified: "h ow much does the uncertainty in the astrophysics (foreground) propagate in to the power spectrum of 21cm intensity fluctuations?"\n\n[15:27] Efficiently modeling the astrophysics : "the most natural way to do this seems to be by using a halo model f ramework" for associating baryonic gas with dark matter halos\n\n[17:44] < a href="https://youtu.be/K8bS_52_XMk?t=1064">The HI halo model and its fre e parameters\n\n[25:02] Available HI data\n\n[27:54] Constraints\n\n[28:54] Best fit halo model\n\n[31:04] Insights\n\n[36:46] Cosmology and astrophysics constraints: precision and accuracy\ n\n[37:50] CO contraints: z ~ 0.3\n\n[38:14] A halo model for carbon monoxide\n\n[40:54] Reverse engineering: "Abundance matching\; combine HI con straints with empirical evolution of stellar-halo relations"\n\n[42:36] Stellar mass buildup: Comm entary on Figures 2 and 4 in the paper\n\n[46:20] Summary

\n \n[49:48] Future work \n\n[51:36] Q&A: Outside of your own research\, what are your thoughts on what's most interesting in cosmology currently?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/11/ END:VEVENT BEGIN:VEVENT SUMMARY:Clare Burrage (University of Nottingham) DTSTART:20200605T060000Z DTEND:20200605T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/12 DESCRIPTION:Title: Atomic lab experiments rule out almost all of chameleon dar k energy model-space\nby Clare Burrage (University of Nottingham) as p art of Cosmology Talks\n\n\nAbstract\nClare tells us about how chameleon d ark energy models can be very tightly constrained by simple atomic lab exp eriments (well\, simple compared to particle accelerators and space telesc opes). \n\nChameleon models were popular for dark energy because their non -linear potentials generically create screening mechanisms\, which stop th em generating a "fifth force" even though they couple to matter. This mean s we wouldn't normally see their effects on Earth. However\, in a suitably precise atomic experiment the screening can be minimised and their effect measured.\n\nIn less than five years\, Clare and her collaborators went f rom the idea to the completed experiment\, which rules out almost all of t he viable parameter space where a chameleon model can explain dark energy. Only a tiny sliver of allowed space is left\, albeit at fundamental param eter values that would be natural ones - so maybe the chameleon is hiding right there waiting?\n\nVideo of talk\n\nMost relevant paper: [1812.08244] Experiment to detect dark energy forces using atom interferometry\, by Dylan Sabulsky\, Indranil Dutta\, E. A. Hinds \, Benjamin Elder\, Clare Burrage\, Edmund J. Copeland\n\n
\n\nIndex to Key Parts of the Talk:\n\n[00:02] Shaun's intro to the topic and Clare's work\n\n[01:15] Clare's introductory brief comment s\n\n[01:45] Q&A: what ar e a couple things you'd want viewers to remember about this talk?\n\n[ 02:27] Q&A: what is the backg round motivation to your recent work and to this topic in general?\n\n [04:17] Q&A: In the near past \, what were the specific problems about this?\n\n[06:25] First slide: A Very Old Idea The type s of experiments we're going to talk about is the idea of testing the equi valence principle...What we're going to see is that these theories of dark energy\, or modified gravity\, or scalar fields kind of related to dark e nergy\, give you a reason to expect that under certain circumstances\, lig ht objects or small objects would fall faster than large ones...that they feel an additional force essentially...and the interesting physics is why that only happens under certain circumstances\n\n[07:42] The standard picture: If the New Physics is Li near\n\n[10:55] If the Ne w Physics is Non-Linear: Screening Mechanisms\n\n[12:43] The Chameleon A scalar field with cano nical kinetic terms\, non-linear potential\, and direct coupling to matter . (astro-ph/0309300) \n\n[15:58] Varying Mass Dynamics governed by an effective potential. Non-linearities in the potent ial means that the mass of the field depends on the local energy density.\ n\n[17:04] Chameleon Screeni ng (1412.6373)\n\n[23:2 1] Why Atoms? (1408.1409)\n\n[25:51] Atom Interferometry\n\n[30:17] Atom Interferometry for Chameleons (1812.08244\, Experimen t to detect dark energy forces using atom interferometry)\n\n[32:04] Imperial Experiment\n\n[40:23 ] Combined Chameleon Constra ints (1609.01192 and 1709.09071)\n\n[41:08] Summary\n\n[46:43] Clare's work in large collaboration ato mic experiment proposals\n\n[48:15] Q&A: Where to next?\n\n[49:47] Q&A: Outside of your own research\, what do you think i s the most interesting thing in cosmology at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Amanda Weltman (University of Cape Town) DTSTART:20200611T060000Z DTEND:20200611T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/13 DESCRIPTION:Title: Fast radio bursts and cosmology\nby Amanda Weltman (Uni versity of Cape Town) as part of Cosmology Talks\n\n\nAbstract\nAmanda Wel tman tells us about fast radio bursts (FRBs)\, which have been in the news recently in the context of the "missing baryons". She tells us about that measurement (and her own theoretical work preceding it)\, but also about FRBs in general and how they'll be useful for cosmology.\n\nFRBs are what it sounds like they are\, short bursts of radio frequency radiation detect ed from outside the solar system. We still don't know 100% what their orig in is\, but it is possible at least some of them come from magnetars (neut ron stars with very large magnetic fields).\n\nA very useful property of F RBs is that they have a non-zero dispersion relation in the intergalactic medium\, because they interact with the ionised electrons in that space. T his makes it possible to measure the electron density of the inter-galacti c medium\, and/or to measure how far the FRBs are away from us. In each ca se this is based on how much the frequencies within each FRB have disperse d by the time we detect them.\n\nIf you're a cosmologist looking for a pri mer on FRBs and how they'll be relevant for your research\, this is the vi deo you're looking for.\n\nVideo of talk\n\nFRB theory wiki\n\nRelevant papers:
\n[1909.02821] Probing Diffuse Gas with Fast Radio Bu rsts
\n[1905.07132] Fas t Radio Burst Cosmology & HIRAX
\n[1810.05836] A Living Theory Catalogue for FRBs
\n\n
\n\nIndex to Key Parts of the Talk:\n\n[00:02] Shaun's intro to the topic and Amanda's work: i ncludes her comments as an expert on chameleon theory: e.g.\, the experime nts done to rule out parts of the chameleon phase space\; the original the ory is still alive\; observations have ruled out a lot of alternative dark energy theories.\n\n[02:01] First slide summarizing what fast radio bursts are and why they're useful for cosmology\n\n[04:43] Q&A: what are two simple things you'd want viewers to take away from this talk?\n\n[06:10] What we know about FRBs\n\n[08:38] Dispersion Measure (DM)\n\n[10:46] FRB Implications for Cosmology: implications at different scales: early universe\, late universe\, intermediate scales\; there are m ore implications than what could be listed here\n\n[15:37] Can you get better constraints on curvature using FRBs?\n\n[17:24] D ispersion Measure of the IGM as a function of z\n\n[18:40] Contributions to DM\n\n[21:33] DM(z) can shed light on the "mis sing baryon problem": paper reference - A census of baryons in the Uni verse from localized fast radio bursts\, 2005.13161 \n\n[23:26] Tribute to Jean-Pierre Macquart\, first author of 2005.13161\, wh o recently passed\n\n[24:04] Comments on the 2005.13161 paper: "all the baryons in the IGM tha t we couldn't find\, so to speak\, are found by these FRBs\, an absolutely stunning result... when we wrote this paper (1909.02821) last year showing that this could be theore tically done\, it hadn't occurred to me how quickly it would be don e. The rapid evolution in this field is fantastic." Includes an illustrati ve\, short video.\n\n[26:15] Four localised FRBs and what is known about them: new paper by Bh andari et al.\; much of the discussion is about the fact they all are at the edge of their host galaxies\n\n[31:20] Hydrogen Intensity and Real time Analysis eXperiment (HIRAX): similar to CHIME\, "it's a BA O intensity mapping experiment that has FRBs as one of its science cases"\ n\n[33:15] "South Africa has made a really strong case for radio astronomy"\n\n[34:16] Prototype Array and Outriggers\n\n[ 34:46] Localising FRBs\n \n[35:16] Lessons from FRBs< /a>\n\n[35:41] Q&A: Where to next? (from the viewpoint of a theoretical cosmologist)\n\n[36:15] The FRB Catalogue\, and the FR B Theory Wiki: references - (a) frbcat.org and (b) frbtheorycat.org (pape r - FRBCAT: The Fast Radio Burst Catalogue\, 1601.03547)\n\n[38:04] Q&A: What are some things not yet mentioned where the communi ty should work out what things to look into right away?\n\n[43:43] The importance of priors\n\ n[47:36] Outside of your own research\, what do you think is the most interesting thing in cosmology a t the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/13/ END:VEVENT BEGIN:VEVENT SUMMARY:José Luis Bernal (Johns Hopins University) DTSTART:20200619T060000Z DTEND:20200619T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/14 DESCRIPTION:Title: How to tell if your cosmological approximations are accurat e\nby José Luis Bernal (Johns Hopins University) as part of Cosmology Talks\n\n\nAbstract\nJose tells us about how we can make sure our predict ions from cosmology models can be both precise *and* accurate.\n\nVideo of talk\n\nPaper1: [2005.10384] Beware of commonl y used approximations I: errors in forecasts\, by Nicola Bellomo\, Jos é Luis Bernal\, Giulio Scelfo\, Alvise Raccanelli\, Licia Verde\n\nPaper2 : [2005.09666] Beware of common ly used approximations II: estimating systematic biases in the best-fit pa rameters\, byJosé Luis Bernal\, Nicola Bellomo\, Alvise Raccanelli\, Licia Verde\n\nModified CLASS code\n\nJo se's talk from the Cosmology from Home conference\n\n
\n\nIndex to Key Parts of the Talk:\n\n[00:02] Shaun's intro to the topic and José's work\n\n[01:14 ] José's opening comments on his work and the topic papers\n\n[02:20] Q&A: what are two simple things you'd want viewers to reme mber about this talk?\n\n[03:24] Background details on the motivations for this work\n\n[06:15] Shaun draws parallels to an earlier Kit Gallagher talk\n\n[06:50] Start of José's slides and intro comments on the two papers< /a>\n\n[07:32] From the Preci sion Era to the Accuracy Era: very different concepts\; comments on ob servational and theoretical systematics\, statistical uncertainties\; impo rtance of blind analysis\; two outcomes of systematic errors: bias (shift in the posterior)\, misestimation (change in the shape of the posterior)\; recommendation to use methodology of 1803.04470 (Bernal & Peacock) if you want to be conservative\n\n[13:20] Estimating bias in parameters\n\n[17:20] Case example: Galaxy Clustering\n\n[21:34] Quick summary on nongaussianity \, then continuing on galaxy clustering\n\n[24:07] Case example 1: Cosmic magnification\n\n[30 :54] Exploring 2D biases \n\n[33:51] Case example 2: Limber Approximation\n\n[36:54] Multi-tracer Analysis: can be calculated thanks to the Multi_C LASS code\n\n[42:04] Con clusions\n\n[43:50] Wher e to next?\n\n[44:42] Sh aun's hope for an eventual 'central repository' of summarized information or 'cosmology wiki'\n\n[47:36] Outside of your own research\, what do you think is the most intere sting thing in cosmology at the moment\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/14/ END:VEVENT BEGIN:VEVENT SUMMARY:Natalia Porqueres (Imperial College London) DTSTART:20200703T060000Z DTEND:20200703T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/15 DESCRIPTION:Title: You can get 3D info from quasar Lyman-α absorption lines u sing forward modelling\nby Natalia Porqueres (Imperial College London) as part of Cosmology Talks\n\n\nAbstract\nNatalia speaks about forward mo delling in the context of Lyman-α absorption lines of quasar spectra. For ward modelling essentially takes the initial conditions from your early un iverse model and evolves them forward to give the full observational predi ction of all measurable things\, for those specific initial conditions.\n\ nThis is different to\, e.g.\, having a "summary statistic" of this full s et of initial conditions and/or observations that you extract to constrain your model. An example of a summary statistic might be a bispectrum in th e late universe. The bispectrum captures some of the information lost from the power spectrum due to non-linearity\, but not all. Whereas\, in princ iple\, if the forward modelling is done precisely enough no information is lost.\n\nOf course "done precisely enough" is the crucial phrase and forw ard modelling needs to balance precision with speed. The more common summa ry statistics methods are usually much\, much faster than forward modellin g.\n\nSo\, Natalia presents a new method for evolving non-linearities fast er\, one that in particular does a much better job at capturing under-dens ities than the typical particle-mesh codes. She also shows that this forwa rd modelling technique is able to extract\, statistically\, information ab out the 3D regions between absorption lines because it uses the full set o f (correlated) initial conditions as its set of model parameters.\n\nTalk video: youtu.be/eBQv5gRs2y8\n\n Paper: [2005.12928] A hierarchi cal field-level inference approach to reconstruction from sparse Lyman-α forest data\n\n
\n\nIndex to Key Parts of the Talk:\n\n[00:0 0] Shaun's intro to this forward mo delling topic and Natalia's work\n\n[01:19] Natalia's summary of the 2005.12928 paper: inferring the dark matter distribution from the Lyman-α forest\; improved method i ntroduces a field-based approach to describe the DM dynamics\, more accura te in description of the voids and under-densities\n\n[02:33] Q&A: what are two simple things you'd wan t viewers to remember about this talk?: it's possible to infer 3D info rmation from the Lyman-α forest\, and a field-based approach to describe the DM dynamics has some advantages over the more standard particle-based approach \n\n[03:54] Q&A: the motivation for this work\n\n[06:55] (1) collaborators\, and (2) this work was carried out within t he Aquila Consortium\n\n[07:13] First slide: Forward modelling approach: visual description of the technique\; initial conditons => dynamical model => data model => comp are to real data\n\n[09:55] F rom data to cosmology\n\n[11:20] Data model: fluctuating Gunn-Peterson approximation\n\n[14:23] The BORG framework: Gaus sian prior => dynamical model => data model \n\n[16:15] Propagator Perturbation Theory (PPT): an altern ative to particles: recently developed semiclassical analogue to Lagra ngian perturbation theory (LPT)\n\n[20:53] Comparison LPT and PPT\n\n[22:20] Statistical modular framework\n\n[23:23] Hierarchical annealing with PPT< /a>\n\n[24:41] Testing the m ethod with mock data\n\n[26:42] Interpolation between lines-of-sight\n\n[27:34] Posterior matter power spectrum\n\n[28 :13] Cluster mass profile\n\n[28:48] Void profiles: application - constraint on total neutrino mass\n\n[29:15] Constraining cosmological parameters\n\n[31:14] Velocity field at z > 2\n\n[31:47] Matt er flow\n\n[32:12] Summa ry\n\n[33:33] Q&A: next steps\n\n[35:06] Q&A: ou tside of your own research\, what do you think is the most interesting thi ng in cosmology at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/15/ END:VEVENT BEGIN:VEVENT SUMMARY:Benjamin Giblin (University of Edinburgh) DTSTART:20200711T060000Z DTEND:20200711T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/16 DESCRIPTION:Title: What is KiDS-1000? And why we can trust its results!\nb y Benjamin Giblin (University of Edinburgh) as part of Cosmology Talks\n\n \nAbstract\nBen Giblin tells us about the in-process KiDS-1000 results rel ease. At the time this video is released the collaboration have satisfied themselves that their data is robust and passes all relevant consistency c hecks\, but haven't yet released any cosmological results. \n\nIn fact\, t heir cosmological results are still blinded\, but the consistency remains for all possible unblinded results. So whatever the results are\, they're consistent.\n\nI'm not an observer\, but I found Ben's discussion of thing s like "point spread functions" and "shear ratio null tests" to be very cl ear and understandable - in fact much\, much clearer than what I'm used to from talks like this 😅.\n\nPaper: [2007.01845] KiDS-1000 catalogue: weak gravitational lensing shear measurements\n\nPaper on redshift measurements using self organised ma ps: arxiv.org/abs/1909.09632\n\n
\n\nIndex to Key Parts of the Talk:\n\n[00:01] Shaun's intro to the topic and Ben's work< /a>\n\n[00:54] Ben's opening c omments on this work: series of tests\; modeling of the point spread f unction\; redshift distributions\; some new findings\n\n[03:01] Q&A: what are two simple things you'd w ant viewers to remember about this talk?: (1) the new data release has gone through a lot of rigorous testing and found to be robust\, and (2) d on't just copy the equations in other papers without proving them to yours elf\n\n[03:29] Q&A: what is t he motivation for this work?: measure cosmological parameters from the weak lensing signal: cosmic shear\, galaxy-galaxy lensing\, and galaxy cl ustering\; the benefits of weak lensing as a low redshift probe in compari son to Planck as a very high redshift probe\n\n[06:13] The details of KiDS-1000 and Ben's recent paper< /a>: KiDS-North and KiDS-South\; improvements on this data since the previ ous data release: photometric redshift calibration\; paper references belo w are to the first paper that has come out as of the date of this talk: [2007.01845] KiDS-1000 catalogue: weak gravitational lensing shear measurements\n\n[08:14] Table comparing 3 surveys: KiDS\, DES\, a nd HSC\n\n[08:46] Weak le nsing cosmology: the state of play: KiDS measures a lower S8 than the other 2 surveys\; tension between KiDS and Planck ~2.5σ\; comments on oth er papers\; this tension with Planck disappears if KiDS uses COSMOS2015\, which is used by DES and HSC to calibrate their redshifts\; ongoing debat e\n\n[13:42] KiDS-1000: How t o make sure our shear and redshift estimates are accurate: Null tests of the PSF modelling\; Null-tests of the joint shear and redshift data\n\n [14:16] PSF Modelling: th e "effective PSF" describes how the light of a point source would spread o ut due to atmospheric\, telescope\, and camera effects\; the challenge of weak lensing\; how it's modelled\; comments on Fig. 2 of paper\n\n[18:00] PSF Modelling is hard: d etails on 3 different prescriptions in the literature\; caution on 2 & 3 potentially biasing cosmological inference (e.g.\, S8)\; correlation funct ions comments\n\n[23:20] Fir st-order PSF Systematics Model\n\n[26:24] Flux/spatial dependent PSF systematics model: accoun ting for imperfections in the CCD chips (section 3.4.1 in paper\, Fig. 4)\ n\n[29:29] PSF modelling tak eaways\n\n[30:08] Tests of the joint shear-redshift data\n\n[30:28] Galaxy-Galaxy Lensing (GGL): how shapes of backgro und galaxies are correlated with positions of foreground lensing galaxies\ ; typically causes a tangential shear pattern\n\n[30:55] Using GGL to detect additive systematics in t he shear: see section 4.2 in paper\, Fig. 10\; a new test that they ad vocate\n\n[34:10] GGL to tes t the joint shear-redshift measurements\; comments on Fig. 11 of paper \n\n[39:14] Shear-Redshift N ull-Test Takeaways\n\n[39:30] Main Takeaways: 3 points but one wasn't mentioned earlier: this is a neat example of a blind paper - 3 versions of the data\, one is the t rue data\, other 2 are fake but derived from original data and modified\; see red comments in the paper for blinding details\; cosmological constrai nts will soon be released both from cosmic shear and 3x2pt cosmological an alyses\n\n[42:46] Q&A: Next Steps\n\n[45:00] Q&A: ou tside of your own research\, what do you think is the most interesting thi ng in cosmology at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/16/ END:VEVENT BEGIN:VEVENT SUMMARY:Simon Birrer (Stanford) DTSTART:20200716T060000Z DTEND:20200716T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/17 DESCRIPTION:Title: TDCOSMO H0 results with more data and fewer approximations< /a>\nby Simon Birrer (Stanford) as part of Cosmology Talks\n\n\nAbstract\n Simon tells us about the strong lensing time delay measurements of the Hub ble constant performed by TDCOSMO. \n\nIn the recent paper he has relaxed assumptions about the density profiles around the lenses. Specifically\, i n this analysis it is no longer assumed that the density follows a power l aw\, or NFW profile. This naturally widens the error bars on the measureme nt because the "mass sheet degeneracy" is no longer pinned down.\n\nIn ord er to pin this degeneracy back down they use kinematic data from the lense s to model the density profile. They also calibrate their model on an addi tional external data set of strong lenses. When using just TDCOSMO lenses the central value stays the same\, but when adding the new "SLACS" lenses\ , the measured value of H0 drops to be almost exactly the same as the Plan ck value. Cat\, meet pigeons.\n\nSimon also goes into what the future will look like and what data is needed to bring the accuracy of TDCOSMO back t o what it was before these assumptions were relaxed.\n\nSimon: https://sib irrer.github.io/\nThe paper: https://arxiv.org/abs/2007.02941\nThe analysi s pipeline: https://github.com/TDCOSMO/hierarchy_analysis_2020_public\n\n< hr>\n\nIndex to Key Parts of the Talk:\n\n00:00 Shaun's introduction\n\n01:23 Simon's opening comments: the key that I want people to take away from this paper is not the numbers themselves but the methodology and the possibility to add new data\; there is a huge pot ential on how we can utilize this type of framework to move forward \n\n02 :53 Q&A: is there another tak e away message from this talk that you'd like to mention?\n\n04:44 Time-delay cosmography: equa tion components\; geometric quantities\; if source is variable\, there is a "time-delay" between the multiple images\; this method provides a physic al anchor of the scales at intermediate redshifts\, independent of CMB and distance ladder\; delay is from a few days to a few months (110 days is l ongest in current sample) \n\n06:59 TDCOSMO project: new collaboration of H0LiCOW + STRIDES + SHA RP + COSMOGRAIL projects\; 7 lenses analyzed to date\n\n07:55 Single lens - multiple data: basic in gredients: high resolution imaging to measure and describe in detail the d istortion of the lensing effect\; time delay measurements\; stellar kinema tics\; line of sight contribution\; different telescopes involved\n\n10:31 Forward modeling in action: reconstruct lensing phenomena from the imaging data\n\n11:02 Previous results from the H0LiCOW coll aboration: 6 lenses\; blind analysis for all except first\; question o n observed trend of decreasing H0 with increased redshift\n\n12:57 H0 measurements in flat ΛCDM - perf ormed blindly\n\n13:59 ma ss-sheet degeneracy: see Fig. A.1 and section 2 of paper\n\n15:44 TDCOSMO IV: Hierarchical time-de lay cosmography - joint inference of the Hubble constant and galaxy densit y profiles\n\n16:01 Veloc ity dispersion measurements of the deflector galaxy can break the mass-she et degeneracy: summary of added data\; Fig. 4 in paper\n\n16:58 Constraining galaxy density profil es with lensing and kinematics: SLACS lenses\; have excellent imaging from HST and kinematics from BOSS spectra\n\n17:23 Question and discussion on the assumptions\n\n1 9:02 Returning to discussion on the slides: Fig. 12\, 13b\, 14\, & 17 in paper\n\n26:22 Q&A on details of the modeling\n\n 30:29 More discussion on the mass-sheet degeneracy slide\n\n33:51 Next steps: Fig. 18 from paper\n\n34:34 Way forward 1: data on time delay lenses \n\n35:40 Way forward 2: add ing external data sets\n\n36:44 Way forward 3: challenge yourself\n\n38:40 What is the prognosis for TDCOSMO precision?: optimistic that within a year can get back down to 3% uncertainty\n\n39 :07 Q&A: What do you expect will be the resolution to the H0 issue?\n\n40:27 Q&A: outside of your own research\, what do you t hink is the most interesting thing in cosmology at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/17/ END:VEVENT BEGIN:VEVENT SUMMARY:Eva-Maria Mueller (Oxford) DTSTART:20200720T060000Z DTEND:20200720T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/18 DESCRIPTION:Title: Even BAO alone requires dark energy + cosmology from the la st eBOSS data release\nby Eva-Maria Mueller (Oxford) as part of Cosmol ogy Talks\n\n\nAbstract\nEva-Maria tells us about the cosmological results from the final (cosmology relevant) SDSS/eBOSS data release. eBOSS is a s pectroscopic galaxy survey\, precisely mapping galaxies\, quasars and the Lyman-α forest.\n\nThe two key probes are baryon acoustic oscillations (B AO) and redshift space distortions (RSD). BAO acts as a distance ladder\, and eBOSS now has measurements of BAO at enough redshifts that their data alone constrains the expansion history of the universe precisely enough to prove the existence of a dark energy component. The RSD measurements prob e the growth of structure\, but are unable to resolve any tension between weak lensing measurements and the CMB\, with their results lying right bet ween the two alternatives\, consistent with both.\n\nThe distance scale in BAO can also be anchored using constraints from big bang nucleosynthesis (BBN) allowing eBOSS to infer the expansion rate of the universe today wit hout reference to the CMB. Their measurement is consistent with the CMB an d inconsistent with the local distance ladder measurements (e.g. SH0ESS).\ n\nThe BAO\, RSD and CMB are all consistent with the time evolution of the (unanchored) supernovae so all these data sets can be combined to give an overall constraint. This gives very tight bounds on any deviations from a cosmological constant in ΛCDM\, and on any deviations from a flat geomet ry within our observable universe.\n\nThe next stage in spectroscopic surv eys is DESI\, and then Euclid. COVID permitting\, we should have the first results from DESI within three years.\n\nEva-Maria's Oxford page \n\nThe paper : [2007.08991]The Completed SDS S-IV eBOSS: Cosmological Implications from two Decades of Spectroscopic Su rveys at the Apache Point observatory\n\n
\n\nIndex to Key Parts of the Talk:\n\n00:00 Shaun's introduction\n\n00:37 Eva-Maria's opening comments on the paper\n\n01:28 Q&A: what are two simple things you'd want viewers to remember about this talk?\n\n03:24 1st slide: Cosmological results from 20 years of SDSS redshift surveys: different SDSS components\n\n05:31 Sky coverage of eBOSS: all of the da ta was taken with the 2.5m Sloan Telescope in the Apache Point Observatory in Nex Mexico\n\n06:18 What BAO is and how it's being using: 1st main observable\; a preferred sca le in the clustering and distribution of galaxies that can be used as a st andard ruler\n\n06:43 Redshif t-Space Distortions: 2nd main observable\; gives the growth rate of st ructure and is sensitive to the theory of gravity \n\n07:31 A journey of firsts: SDSS made 1st dete ction of BAO signal in 2005\; BAO bump\n\n08:11 BOSS had 1st detection of the BAO signal in the distrib ution of neutral hydrogen from LyA forest in 2013: also in the distrib ution of quasars in 2017\n\n08:28 Q&A discussion on the size and location of the peak: template fit ting\n\n08:58 SDSS BAO Distan ce Ladder\n\n09:47 The gr owth of structure: comparison with Planck 2018 ΛCDM best-fit model\n\ n10:26 The 23-paper release: this talk focused on what is learned about expansion of universe\, cur vature\, mass of neutrinos\, taking the measurements and transforming them into constraints of cosmological parameters\n\n11:12 Dark Energy: Takeaway - a significant detecti on of DE with only BAO data\n\n13:07 Curvature: CMB by itself has large degeneracy between curvatur e and matter\; adding SN gives improvement but still can't tell for sure\; can nail it down by adding BAO\, shows to high precision the universe is flat \n\n14:09 What is the na ture of Dark Energy?: combining different data sets supports the flat ΛCDM model with constant DE \n\n16:21 Hubble Parameter Tension\n\n17:03 Summary diagrams\, step-by-step going through the diff erent contours\n\n18:49 Combination of BAO+BBN breaks degeneracy compared to BAO by itself: cl ear tension with distance ladder H0 measurement\; BAO+BBN (using no CMB in fo) in good agreement with CMB\n\n19:48 allowing DE EoS to vary and combining CMB+BAO+SN (inverse dist ance ladder) gives H0 in agreement with CMB by itself: DE is not an ex planation for H0 tension\n\n21:35 Can rephrase H0 tension as a sound horizon tension\n\n23:14 The BAO analysis is robust: hard to come up with a systematic that would coherently move galaxies in a way that wouldn't move the position of the BAO bump\n\n23:50 sigma8 - Omega_m Discrepancy: Fig. 9 a in paper\; results just from RSD\n\n25:52 Comparing full data sets - SDSS\, DES\, Planck\n\n26:5 9 Constraint on sum of the n eutrino masses: Fig. 13 in paper\; Planck + BAO + RSD + SN constraints is right at minimum edge for IH but not significant enough to rule out IH (though IH becoming less and less likely\; more data needed)\n\n29:47 20 years of cosmology: summ ary of galaxy spectroscopic surveys\; Fig. 14 in paper\n\n31:50 Conclusion: Legacy of BOSS/eBOSS\n \n32:55 Q&A: Is it valid to combine SN with BAO and CMB?\n\n34:53 Q&A: Where to next? What is coming with Stage IV?: DESI and Euclid for spectroscopy\; other things DESI can look at\; CMB-S4\; LSS T (Vera C. Rubin Observatory)\n\n38:38 Q&A: outside of your own research\, what do you think is the mo st interesting thing in cosmology at the moment?\n\nSupplemental info: One- page summary of the cosmology results and implications at the SDSS website \n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/18/ END:VEVENT BEGIN:VEVENT SUMMARY:Simone Aiola (Flatiron CCA and Simons Observatory\, Atacama) DTSTART:20200805T060000Z DTEND:20200805T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/19 DESCRIPTION:Title: ACT+WMAP is as powerful as Planck\; CMB results on ΛCDM ar e robust\nby Simone Aiola (Flatiron CCA and Simons Observatory\, Ataca ma) as part of Cosmology Talks\n\n\nAbstract\nSimone talks about the lates t Atacama Cosmology Telescope cosmology paper(s). He goes into detail at t he beginning about the history of ACT and where it is now\, as well as wha t data was in the latest results. \n\nHe then goes into how the data has b een checked for robustness and how it is sufficiently consistent with WMAP to motivate combining the two data sets (i.e. WMAP for the large scales a nd ACT for the small scales and polarisation). Combined\, WMAP and ACT are as constraining as Planck\, but don't add much additional constraining po wer when added to Planck (they do measure the same sky of course!).\n\nThe ACT polarisation data is sufficiently high in signal to noise that you ca n even make maps of the data that look as clear as the Planck/WMAP tempera ture maps\, which is quite stunning.\n\nThen Simone goes into the final co smological results. Overall\, Planck and WMAP+ACT are mostly consistent. I n particular\, their H0 predictions are very similar. There is a small amo unt of tension that manifests as a different value of the spectral index ( or\, more precisely\, in the ns vs omega_b constraint contours). This is o nly ~2.4 sigma\, so worth keeping an eye on\, but not worth getting too ex cited about yet.\n\nPapers: arx iv.org/abs/2007.07288 and a rxiv.org/abs/2007.07289\n\nData: lambda.gsfc.nasa.gov/product/act/actpo l_prod_table.cfm\n\n
\n\nIndex to Key Parts of the Talk:\n\n 00:00 Shaun's introduction\n\n0 0:37 Simone's opening comments \n\n01:15 Q&A: what are tw o simple things you'd want viewers to remember about this talk?: combi ning WMAP large-scale and ACT small-scale data yields cosmological constra ints at a precision comparable to Planck\; provides a ΛCDM cross-check in dependent of Planck\; Planck and ACT systematics likely very different\; r esults found to be in agreement \n\n02:43 Q&A: what is interesting about ACT that we couldn't just get from Planck?: CMB secondaries and foregrounds are not possible to do w ith smaller telescopes\n\n04:05 Brief comments highlighting the ACT Collaboration\n\n04:42 Some details on the ACT telescope : plot showing ACT's resolution and sky area coverage compared to other CM B missions\n\n05:46 ACT Datas ets: a brief overview of past\, current\, and future ACT datasets\; re sults presented here are based on ACTPol data taken from 2013-2016\; ACTPo l measured polarization\, previous ACT versions did not\; ACT to continue observing through 2021\n\n06:46 Details on the 3 cameras: cross-checks ability - slightly different optics\, different locations in the telescope\; data recorded at 98 and 1 50 GHz\n\n07:39 Q&A on removi ng foregrounds: higher frequency data from Planck used for detecting a ny dust contamination\, though it has no CMB component\; foreground contam ination is small compared to CMB signal at the frequencies used by ACT\n\n 09:19 Shaun's post-recording edit with additional unrecorded comments by Simone about foreground remova l\n\n10:23 ACT DR4 Survey : total map-depth varies across the sky\; noise levels compared to Pla nck\; Fig. 4 (top panel) in 2007.07288\n\n11:32 ACT temperature and E-mode polarization maps at z~1100< /a>: two different points of view of the physics of the last scattering su rface\; comparison with Planck measurements at different scales from ACT\n \n15:22 Regions for power spe ctra: depth of the map variable across the sky\; "deep" and "wide" (sh allower) regions\; effective area\; Fig. 2\; NOTE: Figure referenc es are for 2007.07289 unless otherwise indicated\n\n17:53 Power spectra at 98 & 150 GHz: deep vs w ide plots\; Fig. 10\n\n20:16 CMB-only power spectra: wide patch errors bars on intermediate scales are smaller than for deep (especially visible in EE)\, whereas the deep d oes well in constraining foregrounds\; Figs. 15 and 24\n\n21:54 Parameter-level tests: Fig. 14\; some of the cosmological parameters are being constrained better by TE tha n TT\; no evidence of systematic effects\n\n23:49 ACT DR4 Cosmology: triangular plot comparing WMA P\, Planck\, ACT in 5D parameter space (all 3 have a τ prior in common)\, Fig. 12 in 2007.07288\; ACT vs WMAP/Planck consistent at 2.3-2.7σ\; two expected degeneracies \n\n26:48 Combining ACT+WMAP (baseline) and ACT+Planck: ACT+WMAP breaks som e of degeneracies that are in the 2 data sets independently\; Figs. 17 & 1 9 in 2007.07288\; ACT shows a mild preference for less damping in the sma ll-scale power spectrum than in ΛCDM\; for more info on combining ACT+WMA P\, see section 6.2.2 in 2007.07288\n\n30:51 ACT DR4 H0 Estimate: Fig. 18 in 2007.07288\n\n31:30 < a href="https://youtu.be/Ememq6FnN1U?t=1890">ACT DR4 Cosmology beyond ΛCD M: Figs. 20\, 21\, 22 in 2007.07288\n\n32:53 A_lens finding (consistent with unity) and discussion : Fig. 20 in 2007.07288\; also see section 7.1.1 in 2007.07288\n\n36:2 0 ACT\, WMAP\, Planck: F igs. 14\, 15 in 2007.07288\; ACT prefers a 2.4σ lower first peak in TT\, higher TE\, lower EE\n\n40:02 ACT DR4 Publicly Released: ~0.5TB of data products and 4.5TB of simu lations available at lambda.gsfc.nasa.gov\n\n40:18 Q&A: What comes next?\n\n42:44 Simons Observatory discussion\n\n43:4 1 Q&A: outside of your own r esearch\, what do you think is the most interesting thing in cosmology at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/19/ END:VEVENT BEGIN:VEVENT SUMMARY:Marika Asgari (University of Edinburgh) DTSTART:20200921T060000Z DTEND:20200921T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/20 DESCRIPTION:Title: KiDS 1000 is statistics dominated and in 3σ tension with P lanck cosmology\nby Marika Asgari (University of Edinburgh) as part of Cosmology Talks\n\n\nAbstract\nMarika tells us about the recent Kilo Degr ee Survey (KiDS) cosmological results. These are the first results from Ki DS after they have reached 1000 square degrees.\n\nMarika first explains h ow they know that the results are "statistics dominated" and not "systemat ics dominated"\, meaning that the dominant uncertainty comes from statisti cal errors\, not systematic ones. \n\nShe then presents the cosmological r esults\, which primarily constrain the clumpiness of matter in the univers e\, and which therefore constrain Ω_m and σ_8. In the combined parameter "S_8"\, which is constrained almost independently from Ω_m by their data they see a more than 3σ tension with the equivalent parameter one would infer from Planck.\n\nMarika's website: https://www.roe.ac.uk/~ma/\n\nPapers: 2007.15632 and 2007.15633\n\nK iDS webinar\n\n
\n\nIndex to Key Parts of the Talk:\n\n00:00 Shaun's introduction\n\n00 :40 Marika's opening comments about two of the five recent KiDS papers: also see the KiDS Key Facts segment beginning at 10:39\n\n01:24 Q&A: what are two things you'd want viewers to remember about this t alk?\n\n02:13 Q&A: what w as the motivation for this work?: the strength of cosmic shear in gene ral is that it rather directly measures the amount of matter compared to s urveys that use galaxy positions\; KiDS is a unique survey in that there's a good handle on the systematics\; also see segment starting at 08:50\n\n 03:12 Q&A: What was done and what are the results? \n\n04:20 Cosmic shear 101 \n\n06:47 Modeling \n\n07:47 Blinding \n\n08:50 Sta ndard cosmological model \n\n10:39 KiDS: Key Facts \n\n11:32 Results: comments on Fig. 5: (all figure references are to 2007.15633 until discussion on the 2nd paper begins at 27:17)\n\n13:01 Two point statistics and their s cale sensitivity\n\n13:40 Comments on the 4 panels of Fig. 1 from 2007.15633\n\n17:39 "Headline plot"\, comments on Fig. 6< /a>\n\n19:08 The capital S8 parameter\n\n21:00 Impac t of nuisance parameters: comments on Fig. 7\n\n25:40 Comparison with Planck\, DES\, and HSC: comments on Fig. 9\n\n27:17 Start of discussion on 2nd paper\, 2007.15632All following Figure refe rences from here are for 2007.15632)\n\n27:55 Survey Footprint \n\n28:30 Figure 1: 3x2pt: Cosmic Shear +\n\n29:15 Figure 2: 3x2pt: Cosmic Shear + Clus tering +\n\n29:55 Figure 3\, left panel: 3x2pt: Cosmic Shear + Clustering + Galaxy-Galaxy Lensing \n\n32:47 Figure 6\, rig ht panel: Consistency between probes\n\n33:37 Figure 4\, KiDS - Planck Tension Metrics\n\n35:2 7 Figure 8\, Comparison with other analyses\n\n36:10 Comparison of KiDS core cosmology papers\n\n37:13 Q&A: What's the next big thing in photometric l ensing after what's currently happening?\n\n38:44 Q&A: What are you working on next?\n\n39:18 Q&A: outside of your own res earch\, what do you think is the most interesting thing in cosmology at th e moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/20/ END:VEVENT BEGIN:VEVENT SUMMARY:Bodo Schwabe and Mateja Gosenca (Göttingen U and U of Auckland) DTSTART:20200929T050000Z DTEND:20200929T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/21 DESCRIPTION:Title: AxioNyx - Public code to simulate both Fuzzy and Cold Dark Matter in hires | FDM≡CDM on large scales\nby Bodo Schwabe and Matej a Gosenca (Göttingen U and U of Auckland) as part of Cosmology Talks\n\n\ nAbstract\nBodo Schwabe and Mateja Gosenca tell us about AxioNyx\, which i s a new public code for simulating both Ultralight (or "Fuzzy") dark matte r (FDM) and Cold dark matter (CDM) simultaneously. The code simulates the FDM using adaptive mesh refinement and the CDM using N-body particles. As far as I'm aware it is the first publicly available code that can do both without needing adaptation out of the tin (let me know in the YouTube page comments if I'm missing any codes - sorry :-/ ).\n\nThe code passes a bun ch of sanity/consistency checks\, matching linear theory when it should ma tch and deviating when it should deviate. The paper discussed mainly just introduces AxioNyx\; the new physics will come in future papers. Things Bo do\, Mateja and collaborators will be tackling are: simulations with full cosmological initial conditions for the combination of FDM+CDM\, adding ba ryons (long-term project)\, gravitational heating of stars in FDM halos\, and re-assessment of earlier constraints on FDM with FDM now only a sub-fr action of the total dark matter content (e.g. the Lyman Alpha constraints) . Stay tuned\, and/or get in touch with them if you're keen to help make a ny of that happen :-).\n\nOne neat result from this paper was the confirma tion of the "Schrodinger-Vlasov" correspondence. This essentially says tha t FDM and CDM will behave equivalently on large enough scales. On smaller scales the fuzziness of the FDM causes it to deviate (essentially\, it is so light that its deBroglie wavelength is astrophysically relevant). This correspondence has been shown statistically\, and as a limiting result\, i n earlier papers but this is (as far as I'm aware) the first paper where t he FDM and CDM are in the same gravitational potentials in the same simula tion and one can see them do the same stuff on large scales. It wasn't sur prising\, but it's still good to check and see it happen. \n\nThe most int eresting things happen when the proportions of FDM and CDM are similar (i. e. when one doesn't just dominate the other entirely)\, which might be an interesting thing for considering in future papers too.\n\nBodo: https://bodoschwabe.github.io/
\nMa teja: https: //uk.linkedin.com/in/mateja-gosenca-99b267133\n\nAxioNyx: https://github.com/axionyx
\nThe paper: https://arxiv.org/abs/2007.08256< /a>\n
\n\nIndex to Key Parts of the Talk:
\n00:00 Shaun introduces Bodo Schwabe and Mateja G osenca
\n\n00:37 Mateja '\;s opening comments about this new code
\n\n02:18 Q&\;A: what are two things you'\;d want viewers to remember about this talk?
\n\n03:41 Q&\;A: what was the motivation for this w ork?
\n\n06:36 Q&\; A: What was done in the paper? What are the details about adaptive mesh re finement (AMR)?
\n\n07:05 Slide: FDM Structure Formation
\n\n09:17 Q&\;A: Is there an intuitive way of explaining w hy the Schrodinger equation is the right equation here?
\n\n10:10 < a href="https://youtu.be/ufRKKi6CUUs?t=610">Slide: FDM mass constraints
\n\n14:49 Slide: Quantif ying Mixed Fuzzy Cold Dark Matter Halo Dynamics: Radial density profil es\; CDM velocity dispersion vs FDM granular structure\; Solitonic core dy namics
\n\n16:22 Slide: Ax ioNyx: Simulating Mixed Fuzzy and Cold Dark Matter: Figure 1 from the paper
\n\n17:54 Slide: Sp herical Collapse – linear: Figures 2 and 3 from the paper
\n\n21: 14 Slide: Spherical Collapse – Non-linear: Figure 4 from the paper
\n\n27:26 Slide: Comments on Figures 5\, 6\, and 7 fro m the paper
\n\n32:07 Q&\;A about (1) the linearity and (2) is there an intuitive explanatio n of the equations?
\n\n35:30 Conclusions slide
\n\n38:22 Q&\;A: What is coming next in your work?
\n\n42: 29 Q&\;A asked individual ly to Bodo and Mateja: outside of your own research\, what do you think is the most interesting thing in cosmology at the moment?
\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/21/ END:VEVENT BEGIN:VEVENT SUMMARY:Ryan Keeley (Korea Astronomy and Space Science Institute) DTSTART:20201008T050000Z DTEND:20201008T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/22 DESCRIPTION:Title: Maybe inflation is the solution to the Hubble tension!? \nby Ryan Keeley (Korea Astronomy and Space Science Institute) as part of Cosmology Talks\n\n\nAbstract\nRyan tells us about how the Hubble tension (between Planck measurements of the cosmic microwave background temperatur e anisotropies and SH0ES measurements of the expansion rate of the univers e) can be completely solved with a non-standard primordial power spectrum for the curvature perturbation\, which could arise e.g. if there is a kink in the inflationary potential. \n\nThe non-standard power spectrum has an oscillatory feature that exactly mimics the effects of a slightly differe nt value for the expansion rate today. They find this power spectrum by ex plicitly reconstructing it\, so they aren't supplying a well motivated a p riori model. However their work does represent a proof of concept that a n on-standard power spectrum could mimic the effects of a different expansio n rate.\n\nWhile the Hubble tension remains unsolved and while all other m odels to explain it suffer from their own problems\, work like this remain s well motivated. It would perhaps be a bit fine tuned to have a feature a t exactly the right place in the primordial power spectrum to mimic the ef fects of H0 today\, but there could be many features and if one happened t o align then this would be what we would see\, so it can't be ruled out a priori.\n\nFuture work will test this with polarisation data and the matte r power spectrum... so stay tuned. If this is the solution it might leave measurable signatures in those results.\n\nRyan: http://cosmology.kasi.re. kr/members.php?member=ryan \n\nThe paper: https://arxiv.org/abs/2006.12710 Inflation Wars: A New Hope\n
\n\nIndex to Key Parts of the Talk: \n\n00:00 Shaun's introducti on\n\n01:04 Ryan's opening comments\n\n02:01 What t wo simple things do you want people to take away from this talk?\n\n02 :35 What is the background fo r this work?\n\n03:36 Dec onvolution slide: decomposition is done with the modified Richardson-L ucy deconvolution algorithm\n\n04:19 The transfer function and how it gives the modified initial power spectrum\n\n06:47 Modifie d Richardson-Lucy Deconvolution slide\n\n07:43 Sound Cancellation slide: Figure 1 from the pape r\n\n09:22 Features slide : Figure 2 bottom panel\n\n10:20 Posteriors slide: Figure 3\n\n13:41 Priors slide\n\n18:08 Filtering slide: Figure 4\n\n23:59 Conclusions slide\n\n24:45 Where to next?\n\n26:42 Outside of your own research\, what do you thin k is the most interesting thing in cosmology at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/22/ END:VEVENT BEGIN:VEVENT SUMMARY:George Zahariade (Arizona State University) DTSTART:20201108T050000Z DTEND:20201108T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/23 DESCRIPTION:Title: Quantum gravity adds (v quiet) noise to gravitational wave detectors\nby George Zahariade (Arizona State University) as part of C osmology Talks\n\n\nAbstract\nGeorge tells us what happens in gravitationa l wave detectors when you quantise the gravitational field.\n\nHe talks ab out a calculation he did with Maulik Parikh and Frank Wilczek which examin es what effect quantising the gravitational field would have on gravitatio nal wave detectors.\n\nThey first treat the detector and gravitational fie ld quantum mechanically. For certain gravitational wave states (e.g. a coh erent state\, a squeezed state and a thermal state) they are then able to solve the gravitational field parts of the resulting path integral (or can onical expectation values).\n\nIn the resulting expression they then take the most probable path for the detector (i.e. the classical path) and dete rmine an equation of motion for the distance between the ends of the detec tor (i.e. the classical equation of motion for the detector\, with quantum effects from the gravitational field included).\n\nThis new equation of m otion is like the purely classical one except with the addition of a new n oise term. In the case of a squeezed state this noise can be exponentially enhanced\, which might have implications for gravitational waves from inf lation\, which at least start out in a squeezed state.\n\nGeorge: linkedin.com/georg e-zahariade
\nPapers: 20 10.08208 and 2010.08205
\nEssay: 2005.07211\n\n\nIndex to Key Parts of the Talk: \n\n00:00 Shaun's introduct ion: This is on how one might measure the quantum nature of gravitatio nal waves. Being a bit outside the realm of normal cosmology\, it's at a g eneral technical level so this talk will be at maybe a colloquium level ra ther than a seminar level. \n\n00:42 George's opening comments \n\ n04:44 Q&A: wh at are two things you'd want viewers to remember about this talk?: (1) we predict that the quantization of the gravitational field should imply the existence of an additional source of noise that would superimpose itse lf to all the other noise sources that exist in a GW interferometer\, and (2) the characteristic of this noise depends strongly on the quantum state of the gravitational field\, so the noise it induces on the signal (depen ding on its state) will be very different and possibly observable.\n\n06:0 3 Q&A: what wa s the motivation for this work? \n\n06:50 Q&A: Why hasn't this calculation been done before? \n\n08:53 Could LIGO do something differently now or in the future that w ould be useful to test this prediction?: the signature of the quantiza tion of the gravitational field is a noise term\, so we need an experiment that focuses on the noises not on the signals. \n\n09:11 Getting into the details: First slide - the history of this topic and references\n\n10:00 Outline of the presentat ion \n\n10:54 Basic Idea slide \n\n13:54 Detector Model \n\n16:00 Assumptions and approximations \n\n21:28 De tector response to quantized GW \n\n23:21 Calculating the transition probability f rom the initial states to the final state \n\n24:15 Influence Functional slide : basically this functional encodes all the quantum effects of the gravita tional field \n\n25:46 Able to calculate the influence function for different incoming gravitational field states: first consider a coherent state \n\n29: 16 Analysis o f the Influence Functional slide (for a coherent state) \n\n32:05 Back to the Tran sition Probability slide \n\n33:18 Langevin Equation slide: final result - eff ective equation of motion for the detector including quantum effects\; the quantum modification of the classical geodesic deviation equation\n\n36:0 7 Analysis of Noise slide: for different states there will be different spectra of the noise - equations for vacuum and coherent states\, thermal states\, an d squeezed states\; thermal states might be of interest to cosmologists (s ome stochastic GW backgrounds might be thermal)\; squeezed states of the g ravitational fied can arise from cosmology (inflationary perturbations) \n \n41:07 Estim ates of the noise for each case: the most hopeful scenario is the case of squeezed gravity states that might have a quantum noise that is measur able \n\n42:39 Summary slide \n\n45:08 Q&A: Where to next? \n\n46:15 Q&A: outside of your own research \, what do you think is the most interesting thing in cosmology at the mom ent?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/23/ END:VEVENT BEGIN:VEVENT SUMMARY:Moritz Haslbauer and Indranil Banik (University of Bonn) DTSTART:20201118T050000Z DTEND:20201118T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/24 DESCRIPTION:Title: Maybe Milgromian gravity solves the Hubble tension!? - The KBC void & νHDM model\nby Moritz Haslbauer and Indranil Banik (Univer sity of Bonn) as part of Cosmology Talks\n\n\nAbstract\nMoritz Haslbauer a nd Indranil Banik talk about the Keenan\, Barger and Cowie (KBC) void and the νHDM model of cosmology. \n\nThe KBC void is a locally observed ~300 Mpc scale under-density that appears to be impossible within ΛCDM (under- densities shouldn't have emptied out this much by now).\n\nνHDM is a mode l that has sterile neutrinos as a hot dark matter component and enhanced g ravity in environments with a weak gravitational field. This dark matter a dequately explains the CMB and expansion history of the universe\, but doe sn't cluster on the smallest scales. The modified gravity (essentially Mil gromian dynamics\, or MOND) then kicks in on these scales to produce pheno mena like the correct rotation curves in galaxies.\n\nMoritz and Indranil give an intro to both KBC and νHDM\, and then explain how this model is c onsistent with the main tent-poles of modern cosmology (e.g. the CMB aniso tropies\, nucleosynthesis\, the displacement of the gas and weak lensing i n the bullet cluster\, galaxy rotation curves\, the clustering of galaxies ) and can also alleviate some of the tensions in the standard ΛCDM model. \n\nThe paper: 2009.11292 \ n\nMoritz: moritzhaslbaue r.jimdofree.com \n\nIndranil: Youtube videos \n\nA blog post by Indranil \, Moritz (and co-author Pavel) on the same topic: Big Trouble in a Deep Void\n\nA blog with ongoing updates of the most serious problems for s tandard cosmology: The Da rk Matter Crisis\n
\n\nIndex to Key Parts of the Talk:\n\n[0 0:00] Shaun's intro\n\n[00: 42] Opening comments (Moritz)< /a>\n\n[00:58] Brief summary o f findings Overview: Keenan-Barger-Cowie void and H_0 tension\n\n[03: 36] Take Home Message slide\n\n[04:08] The observation s that motivated this project (Indranil)\n\n[04:34] The most important references and observational constraints\n\n[06:00] T he KBC void and Hubble tension in ΛCDM: the Millennium (MXXL) simulat ion\n\n[09:18] Comments on Fi gure 1 from the paper\n\n[09:46] Why an allowance is needed for redshift space distortion effects\n\n[10:46] One of the impo rtant results is the KBC void falsifies ΛCDM at 6.04σ\n\n[10:59] The redshift space distortion is related to the impact the void has on the locally measured H_0\n\n[11 :56] Observations indicate a deeper underdensity and larger H_0 than is expected in ΛCDM: Figure 2 \n\n[13:22] Large scale failu re of ΛCDM: to get from z=1100 to z=0 observations\, need effectively stronger gravity to grow structure faster\n\n[14:20] Constraints from data on galaxy scales: the secon d motivation for this work\n\n[16:04] Milgromian Dynamics (MOND)\n\n[20:42] Cosmological MOND framework (vHDM): Overview\n\n[23:14] vHDM framework: Impact on CMB\n\n[27:31] Terrestrial Evidence for Sterile Neutrinos\n\n[28:58] Astronomical Evidence for Fast Collisionle ss Matter\n\n[32:28] Wha t the vHDM Framework Can Explain\n\n[34:50] Application to KBC void: Model assumptions (Moritz)\n\n[36:23] Results: Growth of structure: Figure 5\n\n[39:15] Results: Local H_0 & acceleration parameter: Figure 6\n\n[4 3:15] Results: Peculiar velo city field: Figure 8\n\n[45:37] Results: comparing ΛCDM with νHDM \n\n[48:10] Summary and Conclusions\n\n[50:03] What are the next steps? => Out look slide\; simulation videos\n\n[51:14] Q&A on why results from many other void studies aren't g etting large conflicts with ΛCDM\n\n[53:06] Q&A: outside of your own research what do you think i s the most interesting thing in cosmology at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/24/ END:VEVENT BEGIN:VEVENT SUMMARY:Eiichiro Komatsu and Yuto Minami (Max Planck Institute Garching an d KEK Japan) DTSTART:20201123T050000Z DTEND:20201123T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/25 DESCRIPTION:Title: A tantalising hint of parity violation in the cosmic microw ave background\nby Eiichiro Komatsu and Yuto Minami (Max Planck Instit ute Garching and KEK Japan) as part of Cosmology Talks\n\n\nAbstract\nEiic hiro Komatsu and Yuto Minami talk about their recent work\, first devising a way to extract a parity violating signature in the cosmic microwave bac kground (i.e. birefringence) and then measuring it in Planck 2018 data.\n\ nThey get a 2.4 sigma hint of a result\, which is "important\, if true".\n \nThis signal is measured via correlation of E mode and B mode polarisatio n in the CMB. If the universe is birefringent then E mode polarisation wou ld change into B mode and there would be a non-zero correlation between th e two measured modes. Unfortunately\, if the detector angle on the telesco pe wasn't calibrated perfectly this would mimic the interesting signal. Yu to and Eiichiro's new method is to measure this detector angle by looking at the E-B correlation in the foregrounds\, where the light hasn't travell ed far enough to be affected by any potential birefringence in the univers e.\n\nThis allows them to partially distinguish between the two types of m easured E-B correlation. And with this method they get the hint of a signa l for the new physics in the Planck 2018 data.\n\nThe method can be applie d to the data from all other telescopes that have measured the polarisatio n of the microwave background and can therefore be confirmed\, ruled out\, or at least examined by SPT\, ACT\, Polarbear\, etc. \n\nYuto and Eiichir o are also working with Planck to see if they can further rule out other s ystematics\, e.g. an intrinsic E-B correlation in the foreground polarisat ion.\n\nThe paper: 2011.11254 o n the arXiv and published in PRL.\n\nVideo of talk\n\nEiichiro: https://wwwmpa.mpa-garching.mpg.d e/~komatsu/\n\nYuto: h ttps://orcid.org/0000-0003-2176-8089\n\n
\n\nIndex to Key Parts of the Talk:\n\n[00:00] Sha un's intro\n\n[00:38] Open ing comments about the paper by Eiichiro\n\n[01:51] Q&A: What two things would you want people to r emember about this talk?\n\n[03:30] The methodology papers that led to this announcement: they have been working on this for ~2 years\n\n[04:18] How does the electromagnetic wave of the CMB reach us ?\n\n[04:41] Cosmic Biref ringence\n\n[09:24] What was the motivation for this work? Why study cosmic birefringence?\n\n[ 10:17] E- and B-mode decompos ition of linear polarisation\n\n[10:53] Parity flip\n\n[11:30] Power spectra\n\n[12:05] EB correlation from the cosmic birefringence\n\n[14:46] < a href="https://youtu.be/9W9rDlEHg3c?t=886">Searching for the birefringenc e: Improvement #1 (Zhao et al. 2015)\n\n[15:15] The biggest problem: miscalibration of detectors. I mpact of miscalibration of polarisation angles.\n\n[16:10] The past measurements: Uncertainty i n the calibration of α has been the major limitation.\n\n[18:07] The Key Idea: The polarised Galactic foreground emission as a calibrator: it would not be affected by the cosmic birefringence\n\n[18:35] Searching for the birefringence: Improvement #2 (Minami et al. 2019): Idea: miscalibration of the polarisation angle α rotates both the for eground and CMB\, but β affects only the CMB. Key: no explicit modeling o f the foreground EE and BB is necessary.\n\n[20:06] Assumption for the baseline result: What about the intrinsic EB correlation of the foreground emission?\n\n[20:57] Likelihood for the simplest case: single-frequency\, full sky data\n\n[21:08] How does it work? Simulation of future CMB data (Lite BIRD)\n\n[23:18] Questio n that provides an idea for possible follow-up research\n\n[24:20] Application to the Planck Data (PR3): (information for experts)\n\n[25:21] Validation by FFP10 (Planck team's "Full Focal Plane S imulation")\n\n[25:55] M ain Results: Figure 1 from the paper\n\n[27:12] Can we see β = 0.35 +/- 0.14 deg by eyes?: Fi gure 2\n\n[30:00] How about the foreground EB?\n\n[32:31] Q&A: if it turns out to be a systematic error\, what is the most likely error source?\n\n[33:14] Implications: what does it mean for models of dark matter and energy? \n\n[34:19] Conclusion\n \n[38:43] Comment by Yuto on comparison with Planck data\n\n[39:00] What comes next?\n\n[39:56] Q&A: outside of your own research what do you think is the most interesting thing in cosmology at the moment?: Yuto at 40:04 and Eiichiro at 40.13.\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/25/ END:VEVENT BEGIN:VEVENT SUMMARY:Alvaro Pozo (University of the Basque Country) DTSTART:20210213T050000Z DTEND:20210213T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/26 DESCRIPTION:Title: Potential evidence for wave dark matter (via core-halo tran sition in dwarf galaxies)\nby Alvaro Pozo (University of the Basque Co untry) as part of Cosmology Talks\n\n\nAbstract\nAlvaro tells us about a r ecent paper where he an collaborators detect the transition between a core (flat density profile) and halo (power law density profile) in dwarf gala xies.\n\nThe full core + halo profile matches very closely what is expecte d in wave/ultralight/fuzzy/axionic dark matter simulations (without baryon ic effects included). That is\, there is a very flat core\, which then dro ps off suddenly and then flattens off to a decaying power-law profile. The core matches the soliton expected in wave dark matter and the halo matche s an outer NFW profile expected outside the soliton.\n\nThey also detect e vidence for tidal stripping of the matter in the galaxies. The galaxies cl oser to the centre of the milky way have their transition point between co re and halo happen at smaller densities (despite the core density itself n ot being systematically smaller). The transition also appears to happen cl oser to the centre of the galaxy\, which matches simulations.\n\nOf course the core-+halo pattern they have clearly observed might be due to somethi ng else\, but the match between wave dark matter simulations and observati ons is impressive.\n\nThe huge caveat is that the mass for the dark matter that they use is very small and in significant tension with Lyman Alpha c onstraints for wave-like dark matter. This might indicate that the source of this universal core+halo pattern they're observing comes from something else\, or it might indicate that the wave dark matter is more complicated than vanilla models... \n\nStay tuned to the arXiv for future papers look ing at this in more detail!\n\nPaper: 2010.10337\n
\n\nIndex to Key Parts of the Talk:\n\n[ 00:00] Shaun's intro\n\n[00 :38] Alvaro's opening remarks and brief summary of paper\n\n[00:48] Q&A: What two things would you want people to remember about t his talk?\n\n[01:12] Abstr act and Introduction\; main objectives of this work\n\n[02:58] Focus on dwarf galaxies\n\n[04:5 2] Main Two Results\n\n[0 6:55] Context - general info of dwarf galaxies and classification between isolated and orbiting galaxie s\; Table 1 from the 2010.10337 paper\n\n[09:00] Motivation for this work\n\n[12:03] Context: NFW inefficient to describe th e density profile in the centre -> solution: add wave dark matter profile\ ; Plummer model\n\n[14:28] Methodology\n\n[19:17] Explanatory comment insert from Shaun while editing\n\n[21:02] Results\; Figure 5 from the paper< /a>\n\n[24:06] Figure 1 from the paper\n\n[24:58] Fi gure 2\n\n[28:12] Figure 3: "the most important\, or one of the most important plots of the paper" \n\n[31:38] Figure 4 \n\n[36:47] Conclusions\ n\n[41:08] Where to next?\n\n[42:49] Outside of your own research what do you think are the most interesting things in cosmolo gy at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/26/ END:VEVENT BEGIN:VEVENT SUMMARY:Volker Springel (Max Planck Institute for Astrophysics) DTSTART:20210226T050000Z DTEND:20210226T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/27 DESCRIPTION:Title: Simulating cosmic structure formation with the GADGET-4 cod e\nby Volker Springel (Max Planck Institute for Astrophysics) as part of Cosmology Talks\n\n\nAbstract\nCosmology Talks moderator Shaun Hotchkis s welcomes guest speaker Volker Springel\, who talks about the new GADGET- 4 code.\n\nFeaturing all the things you wanted to know about GADGET-4 but were afraid to ask\, including:\n\n- What new algorithms are used to make it better and faster than earlier versions\n\n- Why you never heard of GAD GET-3\n\n- What new features you can now use when running cosmological sim ulations (e.g. varying the algorithms\; or outputting lightcones\, halo ca talogues and merger trees "on the fly")\n\n- why storing the locations of your simulation particles as integers is better than storing them as float ing point numbers\n\n- and what the author of the most used simulation cod e in cosmology thinks are the most interesting questions in cosmology at t he moment (both related and unrelated to simulations)\n\nVolker Springel: Home page on M ax Planck Insitute site\n\nGADGET-4 code: wwwmpa.mpa-garching.mpg.de/gadget4/\n\nPaper : 2010.03567\n
\n\nIn dex to Key Parts of the Talk:\n\n[00:00] Shaun's intro\n\n[00:45] Volker's opening comments about the paper and the code\n\ n[01:26] Q&A: What two things would you want people to remember about this talk?\n\n[02:48] Diving into the details\n\n[03:51 ] Upcoming extremely large ga laxy surveys promise the next advances in cosmology: EUCLID\, LSST\, W FIRST\; their goals\; accurate theoretical predictions of comparable size as the surveys are needed\n\n[05:32] For GADGET to remain a useful code\, it needed profound upgrades\; what we tried to achieve with GADGET-4\n\n[07:21] Historical evolution of GADGET code\n\n[08:5 2] Recent GADGET history\ n\n[11:36] Comments on the 20 10.03567 paper\n\n[12:55] Simulation output: Millennium-TNG example\n\n[14:33] The new GADGET-4 code scales beyond 10^5 core s\n\n[17:12] GADGET-4 sh ows much better strong and weak scaling as GADGET-2: Figure 61 in the paper\n\n[24:00] GADGET-4 ca n be used in a number of different configurations\n\n[25:01] The fast mulitpole method (FMM)\n \n[26:53] Novel MPI-3 based shared memory parallelization paradigm\n\n[28:08] Scaling of force errors: Fig 10\n\n[30:56] < a href="https://youtu.be/4zFlSP-_C54?t=1856">The optimum multipole order i n terms of CPU consumption: Fig 13\n\n[32:43] Comparison with other codes\n\n[33:51] The tree force approximation: Fig 25/26\, left panel\n\n[35:24] The FMM force field expansions: Fig 25/26\, right panel\n\n[37:25] Integer coordinates\n\n[ 40:42] Lightcones\, merger t rees\, power-spectra\, etc: Fig 41\n\n[43:00] Subhalo tracking\; subhalo catalogues\; merger trees \n\n[47:05] Summary\ n\n[49:00] Where to next?\n\n[52:37] Q&A: outside of your own research what do you think is the most interesting thing in cosm ology at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/27/ END:VEVENT BEGIN:VEVENT SUMMARY:Azadeh Maleknejad (CERN Department of Theoretical Physics) DTSTART:20210310T050000Z DTEND:20210310T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/28 DESCRIPTION:Title: A common origin for inflation\, neutrino mass\, baryogenesi s\, and dark matter\nby Azadeh Maleknejad (CERN Department of Theoreti cal Physics) as part of Cosmology Talks\n\n\nAbstract\nAzadeh talks about a "beyond the standard model" of particle physics framework that appears a ble to simultaneously...\n\n- provide a particle physics backbone to infla tion
\n- give neutrinos mass
\n- generate a dark matter candidate
\n- and solve baryogenesis
\n\n...thus linking all of these cosmologic al problems. The framework can also deal with various particle physics pro blems\, such as the origin of the accidental B-L symmetry in the standard model\, the strong CP problem\, and the vacuum stability problem.\n\nSo\, it's safe to say that if the framework survives scrutiny it is a massive a chievement.\n\nThe framework takes ideas from the "neutrino minimal standa rd model"\, specifically a new SU(2) gauge field that couples only to righ t handed particles and can generate neutrino masses\, as well as provide a dark matter candidate via the lightest right handed neutrino.\n\nIt then combines those ideas with some from Azadeh's earlier work creating the mod el of gauge-flation. Specifically\, it allows for the fields that interact under this new SU(2) gauge symmetry to be actively generated during infla tion. This allows the vacuum fluctuations present during inflation\, and w hich generate the curvature perturbation\, to also generate the particles that will decay to dark matter and to generate the asymmetry in baryon num ber that eventually becomes the matter asymmetry.\n\nWhat's more\, the mod el makes a number of specific predictions. The primordial gravitational wa ves from inflation would have some non-Gaussianity and will be chiral. And \, the dark matter mass will be ~GeV - and would thus generate gamma rays in regions of very large dark matter density.\n\nIt will be fascinating to see how this framework develops\, and whether numerical reheating studies can shed light on the various particle production processes that generate the matter and dark matter during and after inflation...\n\nAzadeh: https://theory.cern/rost er/maleknejad-azadeh\n\nThe paper: SU(2)R and its Axion in Cosmology: A common Origin for Inflation\, Cold Sterile Neutrinos\, and Baryogenesis [2012.11516]\n\n
\n\n Index to Key Parts of the Talk:\n\n[00:00] Shaun's intro\n\n[00:26] Azadeh's opening comments about the paper\n\n[01:10] < a href="https://youtu.be/oiH64cGQyCE?t=70">Q&A: What two things would you want people to remember about this talk?\n\n[01:59] Q&A: What was the motivation for this work? Wha t has changed based on this research?\n\n[03:13] Getting into the details\n\n[03:51] Curious cosmological coincidences\n \n[04:30] Some conceptual iss ues in the SM of particle physics\n\n[06:17] The kinds of questions that Azadeh tried to answer in this project\n\n[06:58] W hat do Gauge Fields do in Inflation?\n\n[07:43] Does it come with a cosmological signature?\n\n [08:49] How the Inflaton and its Gauge Field are connected to the SM?\n\n[09:44] Is there a simple\, elementary\, & minimal set- up that can explain these cosmological and particle physics issues?\n\ n[11:04] Primordial gravitati onal waves\n\n[12:30] Ori gin of matter asymmetry\n\n[13:36] Baryogenesis via Leptogenesis\n\n[16:56] Origin of neutrino mass and a dark matter parti cle nature possibility\n\n[19:54] Why Gauge Fields in Inflation?\n\n[20:43] SU(2)-Axion Model Building\; Gauge-flation and the Chromo-natural model\; now ruled out by the data\; minimal scenar io of SU(2)-axion inflation\n\n[24:45] Left-Right Symmetric Model\n\n[27:23] SU(2)R-Axion Inflation\n\n[31:02] SU(2)R Gauge Field Production by Axion< /a>\n\n[34:05] New Tensorial mode & Chiral GWs\n\n[35:04] Novel Observable Signature: CMB\n\n[35:57] Parity Odd CMB Correlations: TB & EB != 0\n\n [38:11] Right-handed Lepton & Quark Production by SU(2)\n\n[39:48] Summary of the Mechanism\n\n[44:34] Compare the Minimal Set-up to SU(2)R-Axion Infl ation\n\n[46:51] Q&A: Wh ere to next?\n\n[51:20] Q&A: outside of your own research what do you think is the most interestin g thing in cosmology at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/28/ END:VEVENT BEGIN:VEVENT SUMMARY:Scott Melville and Johannes Noller (Noller: ICG at Portsmouth\; Me lville: Cambridge) DTSTART:20210325T050000Z DTEND:20210325T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/29 DESCRIPTION:Title: Unitarity\, causality & locality: impacts on dark energy an d gravity's speed\nby Scott Melville and Johannes Noller (Noller: ICG at Portsmouth\; Melville: Cambridge) as part of Cosmology Talks\n\n\nAbstr act\nJohannes Noller and Scott Melville talk about their recent paper expl oring the impacts of certain positivity bounds on cosmological parameters. \n\nPositivity bounds are restrictions on low energy effective parameters that arise from requiring the full high energy fundamental theory to satis fy certain criteria. It is possible to show that if\, e.g. all the interac tions of a full theory satisfies unitarity (conservation of information/pr obability)\, causality and locality\, then a specific class of low energy theories must have the speed of light less than the speed of gravity.\n\nT he specific interactions Johannes\, Scott (and collaborator Claudia) used to show this are interactions between dark energy and standard model matte r.\n\nThis condition actually ends up lying right in the region that obser vations prefer for this model\, effectively cutting the allowed parameter space in half.\n\nPaper: https: //arxiv.org/abs/2103.06855
\nJohannes Noller: https://www.icg.port.ac.uk/author/nollerj/
\nScott Melville: http:// www.scottamelville.com
\nSupplemental Video: https://youtu.be/Z3Lx7VXB78E\n\n
\n\n[00:00] Shaun's intro\n\n[00:46] Noller: overview comments about the paper\n\n[04:24] Melville : two takeaway messages to remember about this talk\n\n[05:47] Noller on the background motivation for this work\n\n[08:52] How this work relates to other papers in this area\n\n[09:05] A final comment on the motivation for this work\n\n[10:21] Q&A : Melville comments on importing particle physics knowledge and understand ing into cosmology to constrain theories like dark energy\n\n[12:59] < a href="https://youtu.be/F7YaeAyz-yg?t=719">Q&A: Why had this not been don e before? \n\n[13:59] Get ting into the details \n\n[16:41] The main idea behind the positivity bounds\n\n[16:57] A discussion on unitarity\, causal ity\, and locality\n\n[19:52] Sean's insert when editing: comments on the reason for the supplemen tary video\n\n[20:54] Bu ildup to the consequence in this specific model that speed of matter <= sp eed of gravity \n\n[24:15] Noller: How these bounds impact current observational constraints\; a c ase study\n\n[31:16] Dat a constraints with the positivity prior\n\n[34:54] Sean's explanatory comment insert during editin g\n\n[36:22] Noller cont inuing the talk\n\n[37:34] Case study: 3 key observations\n\n[43:29] Melville reponds to a question by Shaun\n\n[46:07 ] Final comment by Noller\n\n[46:32] Q&A: Where to n ext?\n\n[47:44] Q&A: Wha t do you foresee over the next 24 months?\n\n[53:04] Q&A: outside of your own research what do you think is the most interesting thing in cosmology at the moment?\n\n\n\nSupplemental Video:\n\n[00:00] Sean's comments on the reason for this supplementary video\n\n[00:46] Melville on the standard procedure for deriving positivity bounds\; a physical picture\n\n[04:17] Two important t hings\; and what causality buys you\n\n[05:15] Unitarity\n\n[06:07] Put both ingredients together\; why causality and unitarity come together to give a positivity statement\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/29/ END:VEVENT BEGIN:VEVENT SUMMARY:Dan Thomas (Queen Mary University London) DTSTART:20210406T060000Z DTEND:20210406T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/30 DESCRIPTION:Title: The first model independent cosmological simulations of mod ified gravity\nby Dan Thomas (Queen Mary University London) as part of Cosmology Talks\n\n\nAbstract\nDan Thomas tells us about recent work firs t creating a framework for describing modified gravity in a model independ ent way on non-linear scales and then running N-body simulations in that f ramework.\n\nThe framework involves finding a correspondence between large scale linear theory where everything is under control and small scale non -linear post-Newtonian dynamics. After a lot of care and rigour it boils d own to a modified Poisson equation - on both large and small scales (in a particular gauge).\n\nThe full generality of the modification to the Poiss on equation allows\, essentially\, for a time and space dependent value fo r Newton's constant. For most modified gravity models\, the first level of deviation from general relativity can be parameterised in this way (and w e know that the deviations from general relativity are small because so fa r we haven't found any!!)\n\nThe cosmological simulations are then done by having Newton's constant just vary over time (i.e. it is constant in spac e). This allows them to actually do some simulations\, but in future work they will go beyond this particular simplification.\n\nThey then compare t he simulation results to semi-analytic models like Halofit and ReACT. Halo fit is explicitly just applicable to ΛCDM model but does surprisingly wel l. ReACT however still does much better at fitting e.g. the matter power s pectrum and model Euclid lensing observables.\n\nFuture work will examine more closely why ReACT fits so well and aim to improve the fit even better so that e.g. Euclid and/or the Vera C. Rubin Observatory (LSST) will be a ble to use this method to constrain modified gravity without needing to ru n a new simulation for every step of a Monte Carlo parameter fit.\n\nTheor y framework paper: https://arxi v.org/abs/2004.13051\n\nSimulation paper: https://arxiv.org/abs/2103.05051\n\nDan: https://danbthomas1.wixsite.com/resea rch\n\n
\n\n[00:00] Sha un's intro\n\n[00:40] Dan' s summary comments about the paper\n\n[01:15] Q&A: What are two takeaway messages to remember about this talk?\n\n[01:54] Q&A : What is the specific motivation for this work? What was unsolved? Why di dn't it happen earlier?\n\n[03:20] Recap summarizing 15 years work: Model independent modified grav ity in cosmology\n\n[05:30] What's the problem? The elephant in the room\n\n[06:06] Poisson: a clue to the path forward? \n\n[08:06] Getting into the details of the papers (theory and simulation)\n\n[08:22] A tale of two limits\, and the non-linear scale\n\n[11:43] A quick aside\n\n[12:12] GR+LCDM: 2 ingredients: Comment that has relevance on next slide: "there is no intermediate regime in a LCDM cosmology"\n\n[13:01] Post-Friedmann: "master" equations\n\n[17:19] GR + LCDM\n\n[19:50] Back to modified gravity\n\ n[21:40] Building towards so mething that's useful for data analysis: 7 simulations\; Table 1 and F igure 2 in 2103.05051\n\n[27:23] z=0 phenomenology: Figure 7 upper left panel in 2103.05051 \n\n[2 9:28] Lensing observables: Figure 9 in 2103.05051\n\n[33:21] Fitting functions: Figure 3\n\n[36:58] Fitting functions and Lensing: Figure 10\n\n[4 0:59] Where to next?\n\n [44:00] Q&A: outside of your own research\, what do you think is the most interesting thing in cosmolo gy at the moment?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/30/ END:VEVENT BEGIN:VEVENT SUMMARY:Steffen Hagstotz (Stockholm University) DTSTART:20210422T060000Z DTEND:20210422T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/31 DESCRIPTION:Title: The Hubble parameter measured with Fast Radio Bursts\nb y Steffen Hagstotz (Stockholm University) as part of Cosmology Talks\n\n\n Abstract\nSteffen tells us about how the dispersion measure of fast radio bursts (FRBs)can be used to measure the distance to FRBs. Therefore\, if w e can find the host galaxies of FRBs and measure their redshifts we can me asure the expansion rate (Hubble parameter) with FRBs.\n\nAnd\, he and his collaborators have done just that. At the moment the uncertainty is relat ively large\, but they still get a result within 10% of the more precise m easurements (and consistent with both CMB and supernovae)\, indicating tha t they're doing the right thing.\n\nIn the near future (less than five yea rs) we'll have (hopefully) more than 500 FRBs and a ~% level accuracy meas urement of H0. These are exciting times for FRBs!\n\nPaper: https://arxiv.org/abs/2104.04538\n\nSteff en: https:/ /www.su.se/english/profiles/...\n\n
\n\nIndex to Key Parts of the Talk\n\n[00:00] Shaun's intro\n\n[01:16] Q&A: What two things would you want people to remember about this talk?\n\n[02:06] Q&A: What was t he motivation for this work? What was unsolved? Why wasn't this done earli er?\n\n[03:47] Getting in to the details\n\n[07:40] Overview of Proposed Mechanisms\n\n[09:05] Known FRBs\n\n[10:04] Dispersion measure: basically\, the integrated electro n density along the LoS\n\n[12:52] 3 contributions to the dispersion measure: Milky Way\, LSS\, hos t galaxy\; modeling for each component\n\n[16:21] The LSS component\n\n[18:14] FRB statistics\n\n[22:16] FRB distance scale: baryon density issues\ n\n[26:44] Figure 2 from the 2104.04538 paper: Dispersion measure - redshift relation\n\n[29:47] < a href="https://youtu.be/oHuuzOz68FY?t=1787">Figure 1: Hubble constant con straints\n\n[33:03] The Future: When can FRBs be competitive to measure H0 at the percent level?\n\n[34:02] Figure 3: Expected joint constraints on H0\, the matter density\, and the mean host dispersion measure contribution from a mock sample of 500 FRBs\n\n[36:04] Forecast\n\n[36:36] When do we expect to get to 500 events?\n\n[39:48] What can be done with larger samples\n\n[40:26] Summary\n\n[43:54] What's coming next?\n\n[45:39] A new final question: What current cosmology work do you think is particularly under-appreciated by the community?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/31/ END:VEVENT BEGIN:VEVENT SUMMARY:Peter Coles (Maynooth University) DTSTART:20210502T060000Z DTEND:20210502T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/32 DESCRIPTION:Title: The Open Journal of Astrophysics (and why you should be pub lishing in it)\nby Peter Coles (Maynooth University) as part of Cosmol ogy Talks\n\n\nAbstract\nPeter shares his thoughts on the nature of scient ific publishing and why it is so profitable for the big publishing compani es. Peter isn't a fan of the current state and has taken practical steps t o improve it.\n\nThe biggest practical step he's taken is to create The Op en Journal of Astrophysics. This journal is entirely not for profit runs o ff a $1000 a year budget and (unlike for-profit journals) charges nothing to anyone in the scientific publishing process (authors\, libraries\, etc) . And all the papers it publishes are 100% open access on the arXiv.\n\nT he journal is a fully functioning journal. If you submit a paper there it will get peer-reviewed\, if it is accepted it will get cross-referenced at all the relevant places\, will receive a doi and will have its citations counted at Inspire\, ADS\, etc.\n\nThe journal needs to be running for thr ee years to get an impact factor\, which won't happen until 2022\, but it will be approximately 10-ish (by my extrapolation of his minimum estimate - see video for details) which is very high by astrophysics journal standa rds (if you care about that sort of thing).\n\nAnd... they've already publ ished papers by big consortia like LSST and eROSITA.\n\nIt's a baby step i n overthrowing the early 20th century system we're still using in 2021\, b ut it is at least a step. We should embrace it.\n\nPeter: https://www.maynoothunivers ity.ie/people/peter-coles
\nHis blog: https://telescoper.wordpress.com/
\nThe Journal: https://astro.theoj.org/\n\n
\n\n[0 0:00] Shaun's intro\n\n[01 :43] Peter's opening comments about the Open Journal of Astrophysics (OJAp) \n\n[02:07] Q&A: What two things would you want peop le to remember about this talk?\n\n[03:25] Peter's thanks to Maynooth U for it's support of OJAp\n\n[04:02] The Academic Pub lishing Industry (an exposé!)\n\n[10:10] Why Open Access?\n\n[17:40] Open Access: Green\, Gold\, & Diamond: 3 categori es of open access\n\n[20:34] Peter's comments about the arXiv\n\n[24:51] Why Academic Journals?: the OJAp as an arXiv over lay journal to referee the arXiv submissions\, issue a DOI\, register meta data and citations thru the crossref system\n\n[27:16] The Open Journal of Astrophysics: also note sister journal - the Journal of Open Source Software\n\n[31:02] The author keeps the copyright: w ith most journals\, the author signs the copyright to the journal\n\n[32:3 7] The arXiv id is the DOI i dentifier for all OJAp papers\n\n[32:57] The paper submission process\n\n[34:45] The Journal blog\n\n[35:50] The 6 arXiv astro-ph categories in re lation to the OJAp \n\n[37:30] What the OJAp does\n\n[39:06] What the OJAp does differently\n\n[44:00] In two networks: DOAJ and Free Journal Netw ork\n\n[44:42] Some Stat istics: includes comments on the acceptance rate\, reviewers\, review process\, and issues re fees\n\n[55:23] The future?: much discussion on Journal Impact Factor\n\n[ 01:04:15] How to support the OJAp: e.g.\, consider submitting papers\, refereeing\, and supporting use of the arXiv\; OJAp does not need financial contributions but arXiv d oes\n\n[01:10:26] Q&A: What current cosmology work do you think is particularly under-appreciated by t he community?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/32/ END:VEVENT BEGIN:VEVENT SUMMARY:Eloisa Bentivegna (IBM) DTSTART:20210525T060000Z DTEND:20210525T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/33 DESCRIPTION:Title: Evolution of a periodic eight-black-hole lattice in numeric al relativity\nby Eloisa Bentivegna (IBM) as part of Cosmology Talks\n \n\nAbstract\nEloisa tells us about her work from 2012 (and following year s) constructing a model universe space-time out of lattices of blackholes. \n\nThe motivation for this is to take a very bottom up approach to cosmo logy. We know that around isolated objects the correct metric is close to the Schwarzschild metric\, so in principle the full metric of the universe should be able to be written as a patching together of such metrics. On t he other hand\, the universe on large scales is statistically homogeneous and isotropic and the Friedmann-Robertson-Walker metric appears to fit the data well. \n\nWhat Eloisa and colleagues wanted to know is how these two paradigms come together\, and they more or less found the answer.\n\nEloi sa is also employed not at a university\, or any other institute we might normally expect to find a cosmologist. She is employed at IBM. However\, s he hasn't stopped doing cosmology research\, IBM pay her to do numerical r elativity and cosmology. In the video she talks a lot about how this is po ssible and what IBM want from her as an employee and why this isn't so uni que. In fact\, she's not even IBM's first numerical relativist!\n\nEloisa: https://researcher.watson.ibm.com/researcher/view.php? person=ibm-Eloisa.Bentivegna
\n1st paper: [1204.3568] Evolution of a periodic eight-black-hole latt ice in numerical relativity
\n2018 review article on the topic: [1801.01083] Black-Hole Lattices a s Cosmological Models
\n\n
\n\n[00:00] Shaun's intro\n\n[02:33] Eloisa's historical overview and motivation for this wor k\n\n[04:54] Black hole l attices\n\n[09:54] Initia l choice between two options: (1) keep a zero extrinsic curvature\, bu t choose a conformal metric that's not flat\, vs (2) keep a flat conformal metric but use a non-zero extrinsic curvature\n\n[12:21] Completely analytic initial conditions - huge simplification\n\n[14:45] Special solution - multiple black holes can be obtained by superimposing the fundamental solution\n\n[16:20] Six possible configurations\n\n[17:01] Invert the stereographic projection\n\n[17: 54] Eloisa's email update su bsequent to talk\n\n[19:51] The 8-black hole universe and its full-GR evolution\n\n[21:02] Tools used: Einstein Toolkit an d CosmoToolkit\n\n[21:29] Evolution equations away from the hypersurfaces\n\n[24:14] Plots of some of the observables meas ured during the evolution\n\n[26:26] Status slide\; main conclusions\n\n[28:28] Where to from here?\n\n[32:09] Q&A: Can inhomogeneous but purely G R effects model the H0 tension?\n\n[35:56] Eloisa's role as a computational physicist at IBM\n \n[39:14] Comments on her jo b description\n\n[42:05] Why would a business be interested in basic science? And in cosmology and numerical relativity?\n\n[45:42] A historical trivia example of an early numerical relativity pap er\; first author is an IBMer\n\n[46:58] Q&A: What do you think is an especially underappreciated aspect of cosmology research being done currently?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/33/ END:VEVENT BEGIN:VEVENT SUMMARY:Asta Heinesen and Hayley Macpherson (Canterbury U.\, Cambridge) DTSTART:20210603T060000Z DTEND:20210603T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/34 DESCRIPTION:Title: How much are local anisotropies biasing our measurements (e .g. H0)?\nby Asta Heinesen and Hayley Macpherson (Canterbury U.\, Camb ridge) as part of Cosmology Talks\n\n\nAbstract\nAsta Heinesen and Hayley Macpherson tell us about their recent papers developing a formalism for me asuring local parameters without assuming local isotropy (and homogeneity) and predicting what we should expect for the parameters in this formalism when we go beyond the isotropic approximation of FRW.\n\nAsta talks about her paper from last year which developed the formalism\, and how a finite number of terms can capture all the expected behaviour in the anisotropic luminosity distance\, at each order of redshift.\n\nHayley then talks abo ut how\, together\, they applied Asta's formalism to Hayley's fully relati vistic simulations of cosmology.\n\nThey show the results for the generali sed Hubble\, "deceleration" and jerk parameters. It turns out that when yo u remove the assumption of isotropy these parameters do indeed depend\, so metimes very significantly\, on which direction you look on the sky.\n\nHo w much this is impacting our measurements depends\, among other things\, o n how full your sky coverage is.\n\nAsta: https://inspirehep.net/authors/1726735
\nHayley: < a href="https://hayleyjm.github.io/">https://hayleyjm.github.io/\n\nAs ta's paper: https://arxiv.org/a bs/2010.06534
\nAsta and Hayley's paper: https://arxiv.org/abs/2103.11918\n\nThe paper Hayley mentions where she went as non-linear as possible with full general relati vity: https://arxiv.org/abs/180 7.01711\n\n
\n\n[00:00] Shaun's intro\n\n[01:39] Hayley - quick summary of this work\n\n[02:24] Q&A: What two things would you want people to rememb er about this talk?\n\n[03:33] Asta - background and motivation for this work\n\n[08:12] Review of FLRW models\; "FLRW cosmo graphy"\n\n[10:53] The ge neral geometric case\n\n[12:05] General luminosity distance "Hubble law"\n\n[15:22] Observer congruence\n\n[17:59] Hayley clarifies these are natura lly truncated multipole series\n\n[18:34] Finite set of degrees of freedom\n\n[20:59] The deceleration parameter\n\n[2 2:36] Q&A about luminosity d istance in this work\n\n[25:39] Hayley - background on the simulations: mimicking as closely a s possible the generality of the formalism\, using numerical relativity\n\ n[27:44] Numerical relativty codes\n\n[28:14] Numeri cal relativity for inhomogeneous and anisotropic cosmology\n\n[30:26] A note about smoothing\n \n[33:06] Discussion on gevo lution\n\n[35:14] Commen ts on Figure 1 from the 2103.11918 paper\n\n[37:07] What the cosmological parameters would look li ke for individual observers in the simulations\n\n[39:13] Comments on Figure 3 from the 2103.11918 paper\n\n[43:16] Figure s 2 and 4\n\n[45:08] Ani sotropic contributions: "maximal sky deviation"\n\n[46:29] Exaggerated case of an "unfairly sample d sky": Figures 2b and 5\n\n[49:49] Main take-aways\n\n[53:19] Wrap-up: additional points not previously mentioned\n\n [56:39] Q&A: What do you thi nk is an especially underappreciated aspect of cosmology research being do ne currently?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/34/ END:VEVENT BEGIN:VEVENT SUMMARY:H. Gil Marín\, M. Simonovic\, T. Tröster (U Barcelona\, CERN\, U Edinburgh) DTSTART:20210623T060000Z DTEND:20210623T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/35 DESCRIPTION:Title: What is the best way to analyse galaxy clustering data? Pan el event\nby H. Gil Marín\, M. Simonovic\, T. Tröster (U Barcelona\, CERN\, U Edinburgh) as part of Cosmology Talks\n\n\nAbstract\nThis is a r ecording of a panel event run by the organisers of the Cosmology from Home conference series: https://cosmologyfromhome.com/\n\nThe topic was a co mparison of the relative merits of "full shape" and "template" methods to analyse galaxy clustering data. Essentially the difference comes down to w hether you consider the entire power spectrum as a whole and fit to it in all its glory\, or break into separate pieces that encapsulate specific ph ysics effects.\n\nEach method has its own merits and issues.\n\ nRecorded video on YouTube\n\nT he three panelists were:\n\nHéctor Gil Marín: https://www.ub.edu/bispectrum \n\nMarko Simonovic: https://theory.cern/roster/simonovic-ma rko\n\nTilman Tröster: https://tilman.troester.space\n\nThe papers t hat came up in discussion were:\n\nShapeFit: Extracting the power spectrum shape information in galaxy surveys beyond BAO and RSD: https://arxiv.org /abs/2106.07641\n\nThe Completed SDSS-IV Extended Baryon Oscillation S pectroscopic Survey: N-body Mock Challenge for the Quasar Sample: https:// arxiv.org/abs/2007.09003\n\nThe Completed SDSS-IV extended Baryon Osci llation Spectroscopic Survey: measurement of the BAO and growth rate of st ructure of the luminous red galaxy sample from the anisotropic power spect rum between redshifts 0.6 and 1.0: https://arxiv.org/abs/2007.08994\n\ n
\n\n[00:00] Shaun's intro : this is a new format partially as an experiment for Cosmology from Home but also as an interesting event in it's own right\; the aim is a col laborative pursuit of understanding\, not a debate\n\n[01:32] Intro to the panelists' discussion issue: full-shape vs template methods\; Shaun's video is a little blurry at f irst\, audio is clear\, panelists' video is clear\n\n[04:09] Héctor Gil Marín introduces himself\ n\n[04:53] Marko Simonovic in troduces himself\n\n[05:14] Tilman Tröster introduces himself\n\n[05:33] Shaun: three separate directions to the discussion \n\n[06:26] Héctor: what do we want from a cosmological analysis?\n\n[08:49] Marko: defending the concept of assuming a mod el and doing parameter fits to the model\; not a problem\, a strength of t he full shape analysis approach\n\n[10:52] Responses by Héctor and Tilman\n\n[13:03] Marko - what to do when have systemati cs or bad chi-squared analysis\n\n[14:41] Héctor: fσ8 overview\; what compressing the variables allows\n\n[18:34] Marko - the benefits of full shape analysis\n\n[20:22] Tilman's agreement and further comments\n\n[2 0:58] What info are we gaini ng by getting extra precision on model parameters? Marko response and Héc tor reply\n\n[25:27] Hé ctor on the claim that templates are more model independent\; Marko reply and further discussion based on Figures 2 & 3 from 2106.07641\n\n[37:5 6] Seeking input for a summa ry statement at this point of discussion\n\n[42:36] Héctor on what fσ8 means and what template c orrections may be needed\; discussion\n\n[49:35] Tilman's input on the issues\; further discussion \n\n[52:08] Last questio n: when data isn't independent\, how do you combine the data? \n\n[01: 00:08] If someone in the aud ience wants to work on this\, what is something they could dive into? Also \, what about a template method for the CMB?\n\n[01:03:55] Comments by attendee and co-author Lici a Verde (2106.07641)\n\n[01:07:54] Marko believes next generation surveys will transition to full shape analysis\n\n[01:08:43] In what ways you've gained important insights or changed your mind be tween the pre-discussion and this panel event?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/35/ END:VEVENT BEGIN:VEVENT SUMMARY:Harry Goodhew and Gordon Lee (University of Cambridge) DTSTART:20210802T060000Z DTEND:20210802T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/36 DESCRIPTION:Title: Unitarity constraints on cosmological correlators (valid in *any* flat FLRW metric)\nby Harry Goodhew and Gordon Lee (University of Cambridge) as part of Cosmology Talks\n\n\nAbstract\nHarry Goodhew and Gordon Lee talk about their recent work on “cosmological correlators”. \n\nObservationally these would be power spectra\, bispectra\, etc\; howev er on the theory side they find it easier to work with pieces of the “wa vefunction of the universe”\, which are closely related to observational correlation functions.\n\nThey show constraints on the form these correla tors can take that arise from imposing unitarity during inflation. Contrar y to prior expectations these constraints apply not just in space-times th at are exactly de Sitter\, but in fact in any flat FLRW space-time.\n\nThe most relevant paper: https://a rxiv.org/abs/2104.06587\n\nHarry: https://www.maths.cam.ac.uk/person/hfg23
\nGordon: < a href="https://www.damtp.cam.ac.uk/person/mhgl2">https://www.damtp.cam.ac .uk/person/mhgl2\n\n
\n\n[00:00] Shaun's intro and overview\n\n[01:23] Harry describes the work done in this paper: (H arry's part of the talk)\n\n[02:01] Q&A: What two things do you want people to remember about this tal k?\n\n[02:34] Q&A: The mo tivation for this paper\, and why was this work done now and not earlier? \n\n[03:48 The wave funct ion of the universe\n\n[08:07] Model Based Calculations\n\n[10:51] Bootstrapping: try to directly calculate what the obs ervables are from fundamental principles\; benefits over the model-based a pproach\n\n[12:38] The ultima te goal of the cosmological bootstrap program\n\n[12:53] The most important fundamental principles in the Cosmological Bootstrap\n\n[15:22 Q&A: what about multi-field models?\n\n[16:34] What is unitarity? (Gordon's part of the talk)\n\n[17:52] How to see unitarity?\n\n[19:01] Hermitian analyticity\n\n[21:27] Discontinuity: (culminating in Figure 1 of paper)\n\n[2 6:29] How do we find out if a field is Hermitian analytic?: main result of paper\n\n[28:49] Q&A: What is the implication of th ese results?\n\n[29:08] Manifest Locality\n\n[32:12] Combining unitarity and locality\n\n[33:13] What next?\n\n[37:51] Q&A on observations that would be a consequence of this work\n\n[42:14] Q&A : What is an especially underappreciated aspect of cosmology research bein g done currently?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/36/ END:VEVENT BEGIN:VEVENT SUMMARY:Lloyd E. Knox\, Frances-Yan Cyr-Racine (U of New Mexico\, UC Davis ) DTSTART:20210909T060000Z DTEND:20210909T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/37 DESCRIPTION:Title: A subtle cosmological symmetry & mirror dark sector might f ix H0\nby Lloyd E. Knox\, Frances-Yan Cyr-Racine (U of New Mexico\, UC Davis) as part of Cosmology Talks\n\n\nAbstract\nFrancis-Yan Cyr-Racine a nd Lloyd Knox talk about their work with Fei Ge pointing out a symmetry pr esent in most cosmological observables. \n\nThe symmetry involves rescalin g (almost) *all* the densities and temperatures in the universe thus leavi ng any dimensionless observables unchanged. When exploited it might pave a way to solving the Hubble tension as it allows one to change H0 without c hanging predictions for other crucial cosmological measurements (most of w hich are e.g. temperature\, density\, etc *contrasts* not absolute measure ments). \n\nThe first major road-block is that the CMB temperature is an a bsolute measurement and a very precise one and thus one can't just casuall y change it in one's model\n\nOne way to implement this is therefore to in troduce a mirror dark sector. This allows the measured photons to be uncha nged\, but the overall density of radiation to be rescaled. The mirror wor ld must be very similar to our world so that the exact rescaling happens ( i.e. there must be mirror electrons\, mirror protons\, mirror neutrinos\, etc too).\n\nThere's is one remaining (potentially fatal) flaw\, which is that one must also rescale the photon mean free path near to CMB formation as it affect observables and doesn't change just be adding a dark sector. One way to approach a solution there would be to modify the primordial he lium abundance\, as this would change the density of free electrons at the time of CMB formation. However\, this runs into trouble with observations and would need a model of nucleosynthesis that allows for this change...\ n\n... so this isn't a complete solution at this point\, but definitely so mething to keep an eye on. \n\nMaybe the dark sector affects the helium ab undance\, maybe it changes the free electron density\, maybe something els e can exploit this symmetry and not run into this problem!?\n\nThe model h as just *one* free parameter though and\, at least phenomenologically\, is able to completely solve the Hubble tension - albeit with the creation of a primordial helium tension!\n\nCuriously\, the best fit temperature of t he dark photons is very close to the temperature of the cosmic neutrino ba ckground\, suggesting that *maybe* the production of the mirror world is r elated to neutrino physics somehow.(!?)\n\nLloyd: https://www.lloydknox.com/
\nFrancis-Yan: https://darkuniverse.unm.edu/
\nThe pape r: https://arxiv.org/abs/2107.1 3000
\n\n
\n[00:00] Shaun's intro\n\n[00:50] S ummary overview by Lloyd\n\n[02:17] Q&A: What two things do you want people to remember about this talk?\n\n[03:56] What wer e the motivations for this work?\n\n[05:47] Frances-Yan on the motivations and how this work develo ped\n\n[07:56] Getting in to the details\n\n[08:26] The Hubble constant\, measuring angles and redshifts\, insensitivity of r edshifts/angles to actual distances\n\n[09:34] Invariance of angles under uniform rescaling of the Hubble rate\n\n[10:26] Bu t what if all length scales are uniformly rescaled?\n\n[11:38] Basic geometry and dimensional analy sis\n\n[12:25] Special fe ature of our universe: initial conditions\n\n[14:40] The scaling "recipe"\n\n[16:14] An exact (if unphysical) scaling symmet ry\n\n[17:40] This recip e works - it really leaves the CMB temperature/polarization invariant\ n\n[18:49] Reality check: Sy mmetry breaking\n\n[21:05] Discussion on recombination not being an equilibrium process\n\n[22 :40] Exploiting the symmetry : Mirror World - plus comments on the many mirror sector studies done for other reasons than cosmology\n\n[27:07] Adjusting the photon scattering rate\n\n[29:08] Zeroth Test: The exact symmetry\n\n[31:29] First (real!) t est: Recombination\n\n[32:14] Second test: Compatibility with the cepheid-calibrated distance ladd er (Fig. 1 top left panel from the paper)\n\n[34:55] Mirror Sector Freedom (Fig. 2)\n\n[40:37] Open Questions\; What Comes Next? (comments by both Lloyd and Frances-Yan)\n\n[46:10] Q&A: What work being done in cosmology at the moment do you think is particularly underappreciated? (Frances-Yan) \n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/37/ END:VEVENT BEGIN:VEVENT SUMMARY:Helen Shao\, Francisco Villaescusa-Navarro (Princeton University) DTSTART:20210927T050000Z DTEND:20210927T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/38 DESCRIPTION:Title: Machine learning unveiling cosmology | subhalo masses and t he virial theorem\nby Helen Shao\, Francisco Villaescusa-Navarro (Prin ceton University) as part of Cosmology Talks\n\n\nAbstract\nHelen and Fran cisco (Paco) tell us about their recent work using neural networks to pred ict the masses of subhalos within simulations. They find that the neural n etwork trained on a subset of the subhalos is very good at predicting subh alo masses for the rest of the data.\n\nRestricting themselves to just thr ee parameters\, the radius\, the velocity dispersion and "Vmax" (the maxim um circular velocity of the subhalo) the neural network does almost as wel l. With this as motivation they look for analytic models that might captur e what the neural network is seeing. they find a simple three parameter po wer-law does OK using just radius and velocity dispersion as inputs - but a running power-law with all three (radius\, velocity dispersion and Vmax) does extremely well (almost as well as the neural network).\n\nInterestin gly\, although the neural network starts to perform poorly when extrapolat ed to masses beyond its training set\, the analytical model manages to sti ll perform well. This suggests that they might be on to some genuine new p hysical insight about how these parameters combine to determine a subhalo mass.\n\nVarious subtleties suggest that this new insight might be related to the virial theorem\, but more exploration would be needed to be absolu tely sure how.\n\nThe work here is part of the CAMELS project\, which has thousands of N-body and hydrodynamic simulations of the universe from whic h to train neural networks on.\n\nHelen: https://www.linkedin.com/in/helen-shao-794641169
\nPaco: https:/ /franciscovillaescusa.github.io/
\nCAMELS: https://www.camel-simulations.org/
\n\nThe pap er: https://arxiv.org/abs/2109. 04484
\n\n
\n[00:00] Shaun's intro\n\n[00:59] Summary overview by Helen\n\n[01:21] What two things do you want people to remember about this talk? (Paco)\n\n[02:06] What w as the motivation for this work? (Helen)\n\n[03:53] What are the parameters of interest in this wor k? \n\n[05:30] What some of the parameters mean (Paco)\n\n[07:15] General Methodology (Helen)\n\n[08:23] Symbolic Regression\n\n[09:02] Are the parent halo properties relevan t in this work? (Paco)\n\n[09:33] Continuing with Methodology (Helen)\n\n[13:13] CAMELS-IllustrisTNG (and TNG100/TNG300) vs CAMELS-SIMBA\n\n[15:55] O ther Tests: higher z\, central subhalos vs satellites\, N-body simulat ions\, etc\n\n[17:56] The ne ural network found a universal relation\n\n[20:37] Testing the analytic equations vs the four simu lations\n\n[23:00] Concl usions\n\n[24:15] Physic al Interpretation\n\n[26:10] Questions period\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/38/ END:VEVENT BEGIN:VEVENT SUMMARY:James Alvey (U. Amsterdam\, GRAPPA) DTSTART:20211014T050000Z DTEND:20211014T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/39 DESCRIPTION:Title: Big Bang Nucleosynthesis in 2021\nby James Alvey (U. Am sterdam\, GRAPPA) as part of Cosmology Talks\n\n\nAbstract\nJames Alvey te lls us about the general state of BBN in 2021.\n\nHe gives a really nice p edagogical overview of the physics that goes into BBN calculations relevan t for 2021 observations\, talking through each of the relevant epochs (neu trino decoupling\, the deuterium bottleneck\, etc).\n\nHe gives particular emphasis to the recent LUNA measurements of the D + p →γ + 3He reactio n (or deuterium + proton goes to photon and 3-Helium). This was previously the source of greatest uncertainty in predicting the final deuterium abun dance of BBN.\n\nFinally\, he talks about the implications of the LUNA mea surements on possible new physics beyond the standard model\, in particula r possible thermal relics.\n\nThe Talk: https://youtu.be/Hv8sbRwbSU8
\nThe LUNA paper: https://www.nature.com/articl es/s41586-020-2878-4 (no arXiv version\, I think?)
\nJames' origina l paper on thermal relics: http s://arxiv.org/abs/1910.01649
\nAddendum to James' paper analysing i mplications of LUNA: https://ar xiv.org/abs/2107.11232
\n\n
\n\nIndex to Key Parts of the Tal k:
\n
\n[00:00] Shau n's intro\n\n[00:25] Summa ry overview by James: a theme: why BBN in 2021 is different than BBN i n 2019\n\n[01:52] What two th ings do you want people to remember about this talk?\n\n[03:07] More detail on why this is importan t for us in 2021\n\n[04:59] Comments on the baryon-photon ratio (used interchangeably with the bary on density)\n\n[05:50] Ge tting into the details: What Can You Measure with BBN in 2021?\n\n[06: 23] Why an addendum rather th an a whole new paper?\n\n[07:12] Why Now? Current Status of BBN\n\n[09:29] Q&A on the primordial lithium abundance\n\n[1 0:27] Discussion on nuclear r eaction rate measurements\n\n[13:09] What Quantities Does BBN "See"?\n\n[14:00] The Physics of BBN\n\n[20:40] Solving the Cosmology\n\n[23:19] < a href="https://youtu.be/Hv8sbRwbSU8?t=1399">Temperature-to-Time Relation< /a>\n\n[24:39] Neutrino deco upling\n\n[25:40] Electr on-positron annihilation\n\n[25:50] The BBN Reaction Network\n\n[29:43] Protons and Neutrons: weak freeze-out\n\n[31:0 6] Neutron Decays\n\n[32 :52] The Bottleneck\n\n[ 36:38] Producing Helium-4\n\n[44:46] Describing the Network\n\n[46:42] LUNA and Deuterium\n\n[54:25] Impact on Constraints\n\n[58:02] Summary and Conclusions\n\n[01:01:56] Q&A: What is an especially underappreciated aspect of cosmology research being done currently?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/39/ END:VEVENT BEGIN:VEVENT SUMMARY:Song Huang and Alexie Leauthaud (Princeton and UCSC) DTSTART:20211029T050000Z DTEND:20211029T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/40 DESCRIPTION:Title: Stellar mass in a *single* galaxy's outskirts reveals the * whole* cluster mass\nby Song Huang and Alexie Leauthaud (Princeton and UCSC) as part of Cosmology Talks\n\n\nAbstract\nSong Huang and Alexie Lea uthaud tell us about their new galaxy cluster finder\, which uses the stel lar mass in the outer region of a galaxy as a method to determine the mass of the galaxy's cluster.\n\nIt feels a bit like magic (to me) that the st ars in individual galaxies can be used to weigh the mass of the whole clus ter\, but like other mass proxies one can devise a scaling relationship be tween the proxy and the mass - and then the proof is in the empirical pudd ing.\n\nConcerning that pudding\, Song and Alexie's new proxy has a compar ably small scatter in its scaling relation i.e. when compared to the most common proxy for optical surveys\, the richness (i.e. the number of galaxi es of a certain type in the cluster).\n\nThe most massive clusters found b y this method are also more easily modelled than the most massive clusters found via richness. i.e. there seem to be smaller systematic effects that need to be taken account.\n\nSo\, whatever magic is going on\, it's worki ng!\n\nOverall\, Song and Alexie think a holistic approach to weighing gal axy clusters is the best way to go\, using richness and stellar mass estim ates\, as well as observables from surveys at other wavelengths like X-Ray temperature and the SZ effect on CMB photons that are scattered by hot ga s inside clusters.\n\nIt looks like an exciting\, multiwavelength\, future for galaxy cluster cosmology\, which should further open up a very non-li near distance scale to precision tests of the growth of structure\, modifi ed gravity and the primordial density perturbations.\n\nSong: https://dr-guangtou.github.io/
\nAlexi e: https://alexie.sites.ucsc.edu/
\nThe paper: https://ar xiv.org/abs/2109.02646
\n
\n\n[00:00] Shaun's intro to the work\n\n[00:45] Song's summary\n\n[04:50] Two simple thing to remember about the talk\n\n[06:16] What makes this work relevant in 2021?\n\n[12:18] The details...\n\n[40:33] What comes next?\n\n[46:17] What is particularly underappreciated in cosmology at the moment ?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/40/ END:VEVENT BEGIN:VEVENT SUMMARY:Hironao Miyatake (Nagoya University\, NASA/Caltech Jet Propulsion Lab) DTSTART:20211104T050000Z DTEND:20211104T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/41 DESCRIPTION:Title: Hyper Suprime Cam's (HSC) latest constraints on Ωm and σ8 !\nby Hironao Miyatake (Nagoya University\, NASA/Caltech Jet Propulsio n Lab) as part of Cosmology Talks\n\n\nAbstract\nHironao tells about how t he Hyper Suprime Cam survey collaboration have taken their own data\, and the BOSS data from SDSS to do a joint cosmology constraint.\n\nSpecificall y\, they take the autocorrelation function of the BOSS galaxies and the cr oss-correlation of HSC weak lensing data with the BOSS galaxies to break d egeneracies between cosmology and galaxy bias\, thus allowing the full inf ormation in the galaxy data to be usable (or at least\, lots more of it).\ n\nThey work hard to extract information from the small scales in these tw o probes\, using a cosmology emulator and halo occupation model\, and they include various consistency tests to show that their analysis is robust. (They also did the analysis blind\, to avoid human bias as much as possibl e).\n\nThe final constraints are comparable to recent similar DES and KiDS constraints\, and consistent with both\, but this analysis have a somewha t different degeneracy in the Ωm and σ8 plane.\n\nPersonally\, I'd now l ove to see some sort of combined analysis of all three weak lensing probes as they're all consistent with each other and I expect the combined const raints would be in a lot of tension with Planck (especially because of thi s different degeneracy direction).\n\nHironao: https://sites.google.com/view/hironaomiy atake/home\n\nPaper: https: //arxiv.org/abs/2111.02419\n
\n\n[00:00] Shaun's introduction\n\n[01:47] Two things to remember from the talk\n\n[03:0 5] What is the background?\n\n[05:30] Galaxy-galaxy l ensing x galaxy-galaxy clustering\n\n[11:59] Subaru Hyper Suprime-Cam (HSC)\n\n[14:32] HSC SSP Survey\n\n[17:10] G-g lensing and clustering measurem ents by HSC-Y1 and BOSS\n\n[22:33] Emulator-based halo model\n\n[23:55] Dark Emulator modeling\n\n[26:43] Modeling galaxy-halo connection\n\n[ 32:18] Cosmological inferenc e: systematic tests\n\n[35:38] Cosmological inference: results\n\n[40:52] What is coming next?\n\n[42:42] What is underappreciated by the cosmolog y community?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/41/ END:VEVENT BEGIN:VEVENT SUMMARY:Tilman Tröster (University of Edinburgh) DTSTART:20211115T050000Z DTEND:20211115T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/42 DESCRIPTION:Title: Baryon feedback measured via tSZ (cosmological error bars 5 0% smaller)\nby Tilman Tröster (University of Edinburgh) as part of C osmology Talks\n\n\nAbstract\nTilman tells us about his recent work combin ing KiDS cosmic shear measurements and Planck measurements of the thermal Sunyaev Zeldovich (tSZ) effect from the cosmic microwave background scatte ring off hot gas in galaxy clusters and galaxy groups. The long term goal is to use cross-correlation of shear and the tSZ effect to help constrain (or essentially measure) baryon feedback and thus push to smaller scales.\ n\nIn this work\, they don't push to smaller scales\, partially because do ing so would require many more careful checks and partially because Planck 's beam isn't small enough to make it worthwhile. However they still gain approximately two times tighter constraints in the Ωm vs σ8 plane compar ed to shear alone because of the additional information available in tSZ a bout where matter clusters\, and what the baryons are actually up to.\n\nT he results themselves are awesome (error bars shrinking by a factor of two is impressive enough) but also are a great proof of concept that we can m easure baryon feedback like this (and don't have to necessarily predict it entirely from first principles). \n\nWith CMB Stage 4 beam sizes and sky coverage\, it will be fascinating to see what can be done with this method ...\n\nTilman: https://tilman.tro ester.space/
\nPaper: ht tps://arxiv.org/abs/2109.04458\n\n
\n\n[00:00] Shaun's intro\n\n[00:46] Summary overview by Tilman\n\n[02:04] What two things do you want people to remember about this talk?\n\n[02:56] More background detail on why this is being done now\n\n[0 7:13] Details of what was don e in the paper\n\n[10:02] Q&A on the Cosmic Infrared Background importance in this work\n\n[11: 33] Usage of data from KiDS ( weak lensing survey designed to optimize for gravitational lensing cosmolo gy\; full overlap with VIKING infrared survey)\n\n[13:11] Plot of measured cross-correlation as ang ular power spectrum between KiDS-1000 and Planck data\n\n[13:55] Modelling\n\n[16:59] HMx paper 2005.00009 hydrodynamical h alo model for weak-lensing cross-correlations\n\n[20:08] Applying the model to the data\n\n[22 :40] Joint analysis with cos mic shear\; Fig. 5\, 6\, 9 from paper\n\n[30:01] Systematics and results plots\; Fig. 3\, 7 from p aper\n\n[37:03] Baryon f eedback - intrinsic alignment interaction\n\n[42:21] Where to next?\n\n[43:46] What current cosmology work is particularly under-appreciated by the community?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/42/ END:VEVENT BEGIN:VEVENT SUMMARY:Charles Dalang (University of Geneva) DTSTART:20211124T050000Z DTEND:20211124T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/43 DESCRIPTION:Title: The 4.9σ dipole anisotropy tension *might* be astrophysica l redshift evolution\nby Charles Dalang (University of Geneva) as part of Cosmology Talks\n\n\nAbstract\nCharles tells us about his recent work with Camille Bonvin on the dipole anisotropy tension. \n\nWe expect there to be dipoles in most observables because of our motion through the (stati stically) homogeneous and isotropic universe. However\, there appears to b e a 4.9σ tension between the magnitude of the dipole as measured from the CMB and as measured from quasars in the local-ish universe.\n\nCharles an d Camille have looked at the redshift evolution of the relevant physics th at goes into the local-ish prediction for the dipole. They find that if bo th the magnification bias and the spectral index of the source change with redshift\, the naive expectation for the magnitude of the dipole\, given a particular velocity can change.\n\nTherefore\, they re-derive an alterna tive formula that is explicitly redshift dependent and more easily applied directly to redshift dependent observations\n\nThey look at a sample of q uasars observed by eBOSS to see how the relevant quantities change with re dshift. They do change and Charles and Camille show that *if* the larger o bserved sample of quasars did have the same redshift dependence then the t ension would be substantially reduced.\n\nIt is more difficult to measure the full redshift dependence of the larger quasar sample used to measure t he dipole as they haven't all been measured with one telescope/survey. It is unclear what the actual tension would be between theory and observation were one to be able to take the effect C&C point out into account.\n\nTim e will tell with more detailed and larger surveys...\n\nCharles: https://cosmology.unige.c h/users/charles-dalang\n\nPaper: https://arxiv.org/abs/2111.03616\n\n
\n\n[00:00] Shaun's introduction\n\n[00:58] Charles' introduction\n\n[01:53] Two simple things to take aw ay from the talk\n\n[02:36] What is the background?\n\n[05:05] Source number count kinematic dipole\n\n[06:15] Theory\n\n[10:50] What are the details?\n\n[11:04] Integrating over comoving distance\n\n[13:22] Integrating over redshift\; Figs. 1 and 2 from paper\n\n[17:32] Redshift evolution\; Figs. 3 and 4\n\n[20:43] Theoretical Prediction\; Fig . 6\n\n[22:25] Playing a round\; Figs. 7 and 8\n\n[29:31] Conclusions\n\n[30:33] What comes next?\n\n[32:55] What is under-appreciated by the cosmology community as a whol e?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/43/ END:VEVENT BEGIN:VEVENT SUMMARY:Dillon Brout\, Adam Riess\, Dan Scolnic (Harvard Smithsonian Cente r for Astrophysics\, Johns Hopkins U\, Duke U) DTSTART:20211209T050000Z DTEND:20211209T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/44 DESCRIPTION:Title: SH0ES | H₀ = 73.0 ± 1.0 km s⁻¹ Mpc⁻¹\nby Dillo n Brout\, Adam Riess\, Dan Scolnic (Harvard Smithsonian Center for Astroph ysics\, Johns Hopkins U\, Duke U) as part of Cosmology Talks\n\n\nAbstract \nDillon Brout\, Adam Riess and Dan Scolnic talk about the latest SH0ES me asurement of the Hubble parameter\, making use of the new Pantheon+ supern ovae data set.\n\nThe measurement accuracy has reached ± 1.0 km s⁻¹ Mp c⁻¹\, and they analysed the data in 67 different possible ways and ever y time reach a result that is in significant tension with Planck + ΛCDM. Their baseline analysis\, the one with the best χ² with the fewest free parameters\, is now in 5σ tension\, on its own\, with Planck.\n\nIt isn't clear where the solution to the Hubble tension will come from\, but the f act that all local measurements of H₀ come in above Planck\, and that th e most accurate measurement is now in 5σ tension is very interesting. It' s worth also noting that the prediction from the early universe + ΛCDM do esn't rely uniquely on Planck. Other CMB experiments give the same small v alue\, and even just Big Bang Nucleosynthesis and local Baryon Acoustic Os cillation measurements\, combined with ΛCDM give a small value of H₀. \ n\nSo\, if this isn't evidence of new physics in cosmology\, it will be a very strange series of errors that is causing it.\n\nTalk video\n\nDillon: http://djbrout.github.io/
\nAdam: https://www.stsci.edu/~ariess/
\nDan: https://scholars.duke.edu/person/dsco lnic
\n\nThe paper: http s://arxiv.org/abs/2112.04510\n\n
\n\n[00:00] Shaun's introduction\n\n[01:06] < a href="https://www.youtube.com/watch?v=WFKzEtScvw4&t=66s">Adam's introduc tion\n\n[02:36] Dan and Dillon's additional thoughts\n\n[03:21] Two things to take away from the paper(s) (Adam & Dan)\n\n[05:04] Shaun's intro for diving into the details\n\n[05:21] Pantheon+ Overview: 7 Papers Impr oving upon every major facet of Type Ia SN Cosmology (Dan)\n\n[08:14] The Pantheon+ Compilation of SNe (Dillon)\n\n[11:12] SH0ES 2021 details: First Major Update Since 2016 (>1000 or bits HST) (Adam)\n\n[12:53] SH0ES Distance Ladder Data Sources (Adam)\n\n[17:59] New Cepheid Measurements (Adam)\n\n[19 :11] PSF Photometry\, Artifi cial stars in pipeline measure backgrounds (Adam)\n\n[19:34] Photometry Validation Tests (Adam)\n\n[20:48] Baseline Fit: 3 200 Cepheids\, 300 SN\, non-diagonal covariance - 5 free params (Adam) \n\n[22:29] Baseline Fit: H0 =73.04 ± 1.04 km s⁻¹ Mpc⁻¹\, w/ systematics\n\n[24:50] Baseline Fit: Geometric anchor consisten cy (Adam)\n\n[26:57] Bas eline Fit Residuals vs Background/Crowding (Adam)\n\n[28:51] How to: Simultaneous H0 and H(z) (Ada m\, Dillon-public code will be available)\n\n[32:13] Analysis Variants: 12 categories\, 67 variant s\, bifurcations\, extensions\, etc (Adam)\n\n[36:12] SH0ES Error Budget (Adam)\n\n[37:00] Main Conclusion s\, Summary of new details (Adam)\n\n[37:45] Additional thoughts and discussion (D an\, Adam)\n\n[41:41] Where to next? (All)\n\n[46:14] What do you think is the solution to the Hubble tension?(All)\n\n[50:28] What do you think is under-appreciated by the cosmology community? (Adam\, Dan)\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/44/ END:VEVENT BEGIN:VEVENT SUMMARY:Paco Villaescusa (Simons Foundation) DTSTART:20220110T050000Z DTEND:20220110T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/45 DESCRIPTION:Title: CAMELS - Data Release & Series Introduction\nby Paco Vi llaescusa (Simons Foundation) as part of Cosmology Talks\n\n\nAbstract\nTh is is the first video in a series of videos covering research that the CAM ELS group have done. CAMELS are applying machine learning to cosmology\, u sing a suite of 1000s of simulations to train neural networks\, see what t he networks learn and then try to unveil what it learned in a way we mere humans can understand.\n\nThis video does a brief intro to CAMELS as well as the data release (and how to access the data).\n\nCAMELS: https://www.camel-simulations.org/
\nTalk video: https://youtu.be/6Vgc 72a_VpY
\nPaper: https:/ /arxiv.org/abs/2201.01300\n\nCAMELS talk at Cosmology from Home: https://www.you tube.com/watch?v=NxR_kDlHhGM&\;t=0s
\nPlaylist of CAMELS video s eries: https://www.youtube.com/playlist?list=PLvy7h0l2rJHq03inVPq YnC3llKt0IwwLT\n\n
\n\nIndex to Key Parts of the Talk\n\n[00:00] Shaun's introdu ction to the 8-video series\n\n[01:02] What is CAMELS?\n\n[01:39] What can CAMELS do that normal cosmology can't?\n\n[03 :10] Getting into the detail s (simulations\, algorithms\, code\, parameters)\n\n[05:25] CAMELS in relation to IllustrisTNG\, S IMBA\n\n[06:31] Accessin g the data\n\n[07:22] Te chnical documentation\n\n[08:00] Using Binder\n\n[08:25] Machine learning tutorials\n\n[09:34] Terminology definitions\n\n[11:44] Using Jupyter Notebook example\n\n[1 3:32] What's been done up to now?\n\n[14:45] Future directions\n\n[16:43] H ow to get involved\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/45/ END:VEVENT BEGIN:VEVENT SUMMARY:Paco Villaescusa (Simons Foundation) DTSTART:20220111T050000Z DTEND:20220111T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/46 DESCRIPTION:Title: Cosmology with a single galaxy!? (CAMELS)\nby Paco Vill aescusa (Simons Foundation) as part of Cosmology Talks\n\n\nAbstract\nPaco tells us about how CAMELS have used machine learning to be able to predic t\, with a single galaxy's properties\, the value of Ωm used to simulate the galaxy. \n\nThis is fascinating and if a real physical effect has some far-reaching consequences.\n\n- We might one day be able to learn cosmolo gical parameters by studying the Milky Way
\n- Running a hydrodynamical simulation with the wrong Ωm would mean\, in principle\, that you'll nev er reproduce the exact properties of a galaxy correctly.\n\nCAMELS: https://www.camel-simulations.org/< /a>
\nTalk video: https://youtu. be/4AfjqEj_MaI
\nPaco: https://franciscovillaescusa.github.io/
\nPaper: https://arxiv.org/abs/2201.02202\n\nCAM ELS series overview: https://www.youtube.com/watch?v=6Vgc72a_VpY&\;t=0s
\n Playlist of CAMELS video series: https://www.youtube.com/playlist ?list=PLvy7h0l2rJHq03inVPqYnC3llKt0IwwLT\n\n
\n\nIndex to K ey Parts of the Talk>\n\n[00:00] Shaun's intro\n\n[01:06] Paco's introductory comments\n\n[01:41] What questions were you trying to answer?\ n\n[02:21] Getting into the details\n\n[04:17] Train ing the neural network and testing\n\n[05:56] How correlated are the error bars?\n\n[06:50] Does it work for other paramet ers besides Ωm?\n\n[07:17] Does this really work for all galaxies?\n\n[09:10] The galaxy properties that are responsible for this result\n\n[16:17] What happens if you train on Illustris and test on SIMBA?\n\n[18:07 ] What about environmental dependence?\n\n[20:14] Conclusions and what should the cosmology community take away from this?\n\n[20:54] What would yo u want to discuss with other experts?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/46/ END:VEVENT BEGIN:VEVENT SUMMARY:Jay Wadekar (Institute of Advanced Study) DTSTART:20220112T050000Z DTEND:20220112T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/47 DESCRIPTION:Title: Galaxy cluster mass estimates improved with AI (CAMELS) \nby Jay Wadekar (Institute of Advanced Study) as part of Cosmology Talks\ n\n\nAbstract\nJay tells us about how he has used the CAMELS suit of simul ations to improve upon existing galaxy cluster scaling relations (i.e. tre nds we use to measure cluster masses using observational probes). \n\nOne example is using the concentration of ionised gas in a cluster to add a li ttle bit more precision to a Sunyaev Zeldovich effect - mass scaling relat ion. The value of the concentration makes a small change to the prediction .\n\nJay specifically uses symbolic regression (or similar algorithms) to find expressions that link the properties of interest (e.g. mass\, concent ration and SZ effect)\, thus allowing us as human beings to also gain some intuition from what the machine finds.\n\nJay: https://jaywadekar.github.io/
\nPaper: https://arxiv.org/abs/2201.01305
\nTal k video: https://youtu.be/w_ohkLYMS zs\n\nCAMELS playlist: https://www. youtube.com/watch?v=6Vgc72a_VpY&\;list=PLvy7h0l2rJHq03inVPqYnC3llKt0Iww LT&\;t=0s\n\n
\n\n[00:00] Shaun's Intro\n\n[00:59] Jay's opening comments\n\n[01:48] What is the motivation for this work?\n\n[03:17] Comparison of Machine Learning ap proaches\, starting with deep neural networks\n\n[03:44] Symbolic regression overview\n\n[05:4 0] How symbolic regression w as used in this work\n\n[08:16] Question about the 25 Mpc box size in CAMELS\n\n[11:01] Is the result robust w.r.t. feedba ck prescriptions?\n\n[13:02] Improving the domain of validity of scaling relations\n\n[14:59] Summary and takeaway\n\n [16:01] What would you like to talk about with other experts?\n\n[16:43] Application to other scaling relations?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/47/ END:VEVENT BEGIN:VEVENT SUMMARY:Andrina Nicola (Princeton University) DTSTART:20220113T050000Z DTEND:20220113T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/48 DESCRIPTION:Title: Electron density breaks baryon-cosmology degeneracy (CAMELS )\nby Andrina Nicola (Princeton University) as part of Cosmology Talks \n\n\nAbstract\nAndrina tells us about her work using CAMELS and machine l earning to constrain baryon feedback using the electron density power spec trum. \n\nThe electron density is not itself an observable thing\, but it is a good proxy for observable things like the thermal Sunyaev Zeldovich e ffect and Fast Radio Burst dispersion (or they are good proxies for the el ectron density).\n\nAndrina is able to get nice constraints on baryon feed back and cosmological parameters within the CAMELS simulations. This sort of observational probe of baryon feedback is going to be an important tool for cosmologists if we want to use smaller scales to do cosmology\, and t he sort of connections spotted by Andrina and CAMELS will be valuable for improving these probes.\n\nAndrina: https://www.astro.princeton.edu/~anicola/
\nPaper: https://arxiv.org/abs/2201.04142< /a>
\nVideo of talk: https://you tu.be/D_CLangkIDE\n\nCAMELS playlist: https://youtu.be/D_CLa ngkIDE&\;list=PLvy7h0l2rJHq03inVPqYnC3llKt0IwwLT\n\n
\n\n[00:00] Shaun's intro\n\n[00:51] Andrina's overview comments\n\n[01:40] What is the mo tivation for this work?\n\n[03:44] Getting into the details\n\n[04:03] Constraining cosmology & baryon physics from 2pt-fu nctions (X-ray\, tSZ\, FRBs)\n\n[04:44] How well can the electron density power spectrum constrain both cosmology and baryonic feedback?\n\n[05:32] Simulations (IllustrisTNG and SIMBA)\n\n[06: 35] Plots of the electron po wer spectra from IllustrisTNG & SIMBA simulations (Fig. 1 in paper)\n\ n[08:03] Baryon fraction as predictor of feedback (Fig. 2)\n\n[09:24] Forecasting constraints (Fig. 3 top panels)\n\n[11:1 0] Robustness of constraints to subgrid physics (Fig. 3 bottom panels)\n\n[13:37] Q&A on a common theme among several of the s peakers\n\n[14:53] Summa ry\n\n[16:57] Comments on sample variance in CAMELS\n\n[17:18] Lingering questions and what would you like to discuss wi th other experts?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/48/ END:VEVENT BEGIN:VEVENT SUMMARY:Leander Thiele (Princeton University) DTSTART:20220114T050000Z DTEND:20220114T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/49 DESCRIPTION:Title: Spectral distortions will measure baryon feedback at % leve l (CAMELS)\nby Leander Thiele (Princeton University) as part of Cosmol ogy Talks\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/49/ END:VEVENT BEGIN:VEVENT SUMMARY:Leander Thiele (Princeton University) DTSTART:20220114T050000Z DTEND:20220114T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/50 DESCRIPTION:Title: Spectral distortions will measure baryon feedback at % leve l (CAMELS)\nby Leander Thiele (Princeton University) as part of Cosmol ogy Talks\n\n\nAbstract\nLeander tells us about work using CAMELS simulati ons and neural networks to forecast how well future spectral distortion me asurements will be able to constrain baryon feedback. The answer is "very well" as it seems the measurements of PIXIE would give even % level measur ements of some feedback mechanisms.\n\nLeander: https://phy.princeton.edu/people/leander-t hiele
\nPaper: https://a rxiv.org/abs/2201.01663
\nVideo of talk: https://youtu.be/u2tEG1nLwV8\n\nCAMELS playlist: https://youtu.be/6Vgc72a_VpY&\;list=PLvy7h0l2rJHq03inVPqYnC3llKt0IwwL T\n\n
\n\n[00:00] Shaun 's intro\n\n[00:58] Leand er's overview comments\n\n[01:47] Motivation for this work: baryonic physics is an impediment to c osmology understanding\, e.g.\, huge uncertainty on baryonic feedback mech anisms\, primarily due to AGN and SN\n\n[02:22] Spectral distortions\n\n[03:51] CAMELS feature of small simulation boxes\n\n[04:39] The thermal Su nyaev-Zel'dovich effect\; parameter dependence\n\n[06:25] Forecast constraints\n\n[09:47] Conclusions and takeaways for th e cosmology community\n\n[10:25] To-Do follow-up\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/50/ END:VEVENT BEGIN:VEVENT SUMMARY:Pablo Villanueva Domingo (Instituto de Física Corpuscular) DTSTART:20220117T050000Z DTEND:20220117T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/51 DESCRIPTION:Title: Weighing the Milky Way with AI (CAMELS)\nby Pablo Villa nueva Domingo (Instituto de Física Corpuscular) as part of Cosmology Talk s\n\n\nAbstract\nPablo talks about an actual observational result from CAM ELS\, the measurement of the masses of the Milky Way and Andromeda. The re sults are in agreement with other methods we've used to measure the masses of these galaxies.\n\nPablo: https:/ /pablovd.github.io/
\n\nPaper: https://arxiv.org/abs/2111.14874
\n\nVideo of talk: https://youtu.be/yGdcBrYfs8k\n\nCAMELS playlist: https://youtu.be/6Vgc72a_VpY&\;list=PLvy7h0l2rJHq03 inVPqYnC3llKt0IwwLT\n\n
\n\nIndex to Key Parts of the Talk \ n\n[00:00] Shaun's intro\n \n[00:46] Pablo's overview co mments\n\n[01:59] Weighi ng Dark Matter Halos\n\n[03:04] Is the Milky Way big enough that the baryonic/dark matter ratio is expected to be the same as on a cosmological or galaxy cluster scale? \n\n[05:37] Halos as graphs< /a>\n\n[06:32] Why graph neu ral networks? NN type depends on data structure\n\n[07:55] Inferring halo masses in IllustrisTNG\n\n[09:20] Cross testing in SIMBA\n\n[10:10] Appl ication to the Milky Way and Andromeda\n\n[10:50] Inferring the MW and M31 masses (Fig. 1 of paper )\n\n[14:10] Conclusions \n\n[16:07] Lingering qu estions and what would you like to discuss with other experts?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/51/ END:VEVENT BEGIN:VEVENT SUMMARY:Lucia Perez (Arizona State University) DTSTART:20220118T050000Z DTEND:20220118T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/52 DESCRIPTION:Title: Fixing CAMELS biggest flaw (small box sizes) with semi-anal ytic models\nby Lucia Perez (Arizona State University) as part of Cosm ology Talks\n\n\nAbstract\nLucia tells us about her work with CAMELS tryin g to overcome the biggest barrier CAMELS faces\, small box size. It might never be possible to run 1000s of large volume hydrodynamical simulations simply because the hierarchy of scales is too big (baryon feedback happens on small scales\, overcoming sample variance requires very large boxes). \n\nTherefore\, to get many many simulation boxes\, with baryonic effects in them one option is semi-analytic models. This is what Lucia has and is doing and what she discusses in the video...\n\nLucia: https://isearch.asu.edu/profile/2606833 \n\nPaper: Constraining cosmolo gy with machine learning and galaxy clustering: the CAMELS-SAM suite [2204 .02408]
\n\nTalk video: http s://youtu.be/sx0RCW2p4eU\n\nCAMELS playlist: https://youtu.b e/6Vgc72a_VpY&\;list=PLvy7h0l2rJHq03inVPqYnC3llKt0IwwLT\n\n
\n\n [00:00] Shaun's intro\n\n[ 01:15] Lucia's overview comme nts\n\n[01:49] The massi veness of this work\; why it's still not feasible to do this on a much lar ger scale\n\n[02:12] Vid eo of a simulation\n\n[02:37] How this work fits within the rest of the project\n\n[03:53] Why do this?\n\n[05:34] Science questions\n\n[08:23 ] Getting to smaller scales\ ; neural networks\n\n[09:14] Take-away 1: use more than just two-point statistics\n\n[10:38] < a href="https://youtu.be/sx0RCW2p4eU?t=638s">Issue about summary statistic s\n\n[12:49] Discussion on various meanings of voids\n\n[13:33] How does each statistic perform alone? Or all together?\n\n[15:50] Take-away 2: SA M (semi-analytic model) galaxy clustering measures cosmology well\n\n[ 16:49] Take-away 3: with a SAM\, clustering still feels astrophysics\n\n[18:38] Conclusions\n\n[19:37] The big picture implications and questions.. .\n\n[22:28] What would you like to discuss with other experts?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/52/ END:VEVENT BEGIN:VEVENT SUMMARY:Sultan Hassan (Center for Computational Astrophysics\, Flatiron In stitute) DTSTART:20220211T050000Z DTEND:20220211T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/53 DESCRIPTION:Title: Full non-linear density fields without simulations! (HIFlow /CAMELS)\nby Sultan Hassan (Center for Computational Astrophysics\, Fl atiron Institute) as part of Cosmology Talks\n\n\nAbstract\nSultan tells u s about his work training neural networks on the neutral hydrogen density fields in the CAMELS simulations. \n\nHe uses a process known as normalisi ng flows to find a mapping between the non-linear\, very non-Gaussian 2D p rojected density field and a different Gaussian field. Once this mapping i s found\, the idea is that one can do full statistics on the non-linear fi eld\, by sampling from the Gaussian one. The bold ambition is to use this process to reduce the need for running computationally expensive hydrodyna mical simulations - making it more feasible to get precise cosmological co nstraints from future surveys.\n\nIt's early days in the project\, but the results are already promising as the model is able to generate density fi elds that match both the histogram of density values and the power spectru m (as well as the scatter in both functions) reasonably well.\n\nSultan: < a href="https://sultanier.wixsite.com/website">https://sultanier.wixsite.c om/website\n\nThe Talk: https:/ /youtu.be/wDRd7MojD3I\n\nThe Paper: https://arxiv.org/abs/2110.02983\n\nCAMELS playlist: https://www.youtube.com/playlist?list=PLvy7h0l2rJHq03inVPqYnC3llKt0IwwLT< /a>\n\nCAMELS intro: https://www.youtube.com/watch?v=6Vgc72a_VpY\n\n
\n\n[00:00] < a href="https://youtu.be/wDRd7MojD3I?t=0s">Shaun's intro\n\n[01:29] Sultans's overview comments \n\n[02:26] At what point in training does the model reach a saturation point?\n\n[02:57] What questions were you trying to an swer and why are they important?\n\n[04:10] The main idea of this work\n\n[05:02] Details on how it's done\; addressing th e problems\n\n[07:38] De tails of the results\; Figure 2 from the paper\n\n[10:21] Power spectra and PDFs over the testing set\; Figure 3\n\n[11:05] Normalizing flow\n\n[12:58] Additional details on the power spectra slide\n\n[15:31] Conditioned on Cosmology slide\, Fi gure 5\; comparison between HIFlow and CAMELS\n\n[16:31] Accuracy over all testing set\, R^2 > 90% \, Figure 7\n\n[18:08] Take-aways for the rest of the cosmology community from this work\n\n[ 19:37] What would you like to discuss with other experts inside or outside of CAMELS?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/53/ END:VEVENT BEGIN:VEVENT SUMMARY:Dillon Brout (Harvard Smithsonian Center for Astrophysics) DTSTART:20220301T050000Z DTEND:20220301T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/54 DESCRIPTION:Title: Pantheon+: Cosmology results & Dust\nby Dillon Brout (H arvard Smithsonian Center for Astrophysics) as part of Cosmology Talks\n\n \nAbstract\nDillon Brout tells us about the recent Pantheon+ supernovae ca talogue and cosmology results. The cosmology results are excellent\, inclu ding a factor of two improvement in the "figure of merit" compared to the previous Pantheon result (essentially a halving of error bars). \n\nHoweve r\, the results aren't going to help anyone looking for a clue for a sourc e of new physics. The supernovae themselves appear to follow the ΛCDM mod el very closely. If one anchors them to Planck\, or to the SH0ES Cepheids\ , either way\, one finds tight constraints on beyond ΛCDM parameters like an equation of state "w" or evolution of an equation of state "w_a".\n\nT here is of course the baffling Hubble tension among all of this\, and that is very clearly visible here. Both the Planck+Pantheon and the SH0ES+Pant heon results match up with ΛCDM\, but at different values of H0. Any solu tion to the H0 tension that involves beyond ΛCDM evolution in the late-un iverse appears to be heavily constrained.\n\nThe most interesting part of this talk (for me) was actually the introduction in the answer to "what ne eded to be done before this analysis could happen" (in fact\, this makes u p the largest portion of the talk!). Dillon goes into quite a bit of detai l about an earlier paper he wrote with Dan Scolnic\, examining the affects of dust on supernovae observations. It appears that three of the most imp ortant mysteries in SN analysis were all explainable by the same dust affe ct and Dillon explains why here.\n\nTalk video: https://youtu.be/lVN1-FcCBDc\n\nDillon: https://djbrout.github.io/\n\nPantheon+ cosmology paper: https://arxiv.org/abs/2 202.04077\n\nEffects of dust on supernovae paper: https://arxiv.org/abs/2004.10206\n\n
\n\n Index to Key Parts of the Talk\n\n[00:00] Shaun's intro\n\n[00:57] Dillon's introductory comments\n\n[01:23] Two things for people to remember from th is talk?\n\n[05:14] The motivational and the logistical aspects for this work?\n\n[08:41] Structure formation work based o n supernovae peculiar velocities\n\n[10:17] Why wasn't some of this work done in 2018? Why now?\n\n[11:33] What questions were unsolved that you wanted to address? Figure 4 from the 2202.04077 pap er\n\n[12:03] 3 Lingerin g Mysteries Central to SNIa Cosmology\n\n[12:45] 1. What drives the observed SN colors and color/l uminosity relations?\n\n[14:14] 2. What drives the underlying residual scatter of standardized SNe Ia?\n\n[15:45] 3. What' s driving the evidence for additional standardization?\n\n[17:13] Cepheid calibration question re lating to the number of SN used in this work\n\n[19:19] The SH0ES measurement: host galaxy demogr aphics\, calibrator set of hosts\, distance ladder rung\n\n[20:33] The "aha moment"\n\n[21:04 ] Dust can be the solution to all three mysteries!\n\n[23:08] We can forward the whole sample to learn about SN/Host physics \n\n[25:10] The mass st ep is a consequence of differing dust properties for hosts of different ma sses\n\n[25:35] Dust at tenuation as a function of host galaxy properties\n\n[27:06] Dust is the solution!\n\n[27:38] Predictions from the model \n\n[28:13] What are th e cosmological results in this paper? Figures 4\, 6\; It's important to u se the covariance matrix\n\n[29:43] Constraints on LCDM\, Figure 8\; Consistency with other probe s\n\n[32:02] The data s et with and without SH0ES\; Figure 9\n\n[32:34] Measuring w_a\, the evolution of dark energy\; Fi gure 10\n\n[34:50] Incl uding BAO\; Figures 11\, 12\n\n[35:31] What's next? DES\, LSST\, Machine Learning\n\n[38:36] Comments on the cosmology c ommunity follow-up to this work\n\n[40:49] What current cosmology work do you think is particular ly under-appreciated?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/54/ END:VEVENT BEGIN:VEVENT SUMMARY:Alexandra Amon & Naomi Robertson (University of Cambridge) DTSTART:20220324T050000Z DTEND:20220324T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/55 DESCRIPTION:Title: Lensing & clustering are consistent. Small scales are tough but key to solving S8\nby Alexandra Amon & Naomi Robertson (Universit y of Cambridge) as part of Cosmology Talks\n\n\nAbstract\nAlex Amon and Na omi Robertson talk about their recent work analysing all of the Dark Energ y Survey (DES)\, the Hyper Suprime Cam survey (HSC)\, and the Kilo Degree Survey (KiDS) and the Baryon Oscillation Spectroscopic Survey (BOSS). In p articular they look to see whether the three lensing surveys (DES\, HSC an d KiDS) are consistent with the clustering of galaxies in BOSS.\n\nConsist ency checks are always good just for their own sake\, but this has particu lar relevance in the context of the S8 tension\, as the lensing surveys pr ovide the strongest evidence of this tension.\n\nThey find that the lensin g surveys are (broadly) consistent with each other and are then also consi stent with the clustering in BOSS. When restricting to larger scales\, the y also don't find evidence for a different cosmology to Planck. When they include smaller scales there is a strong tension between the lensing/clust ering probes and the Planck cosmology (i.e. the S8 tension).\n\nTakeaways are that the local probes of matter appear to be consistent with each othe r and the S8 tension is best probed by smaller scales. Unfortunately this is also where baryonic effects dominate so we need more data constraining them and improved modelling to make further progress.\n\nAlex: https://amonalexandra.com/\n\nNaomi: https://www.ast.cam.ac .uk/people/naomi.robertson\n\nTalk video: https://youtu.be/4gjlNyJ0AKY\n\nThe paper: https://arxiv.org/abs/2202.07440\n\n
\n\ nIndex to Key Parts of the Talk\n\n[00:00] Shaun's intro\n\n[01:15] Alex and Naomi's introductory comments\n\n[02:12] Two things for people to rem ember from this talk\n\n[03:43] The motivation for this work\n\n[06:24] State of the art lensing data\n\n[07:20] Challenges with small-scale model ing\n\n[10:00] Clusterin g and Lensing 101\n\n[11:41] Data: Fig. 2 top panel and Fig. 3 from paper\n\n[14:12] Source sample: Lensing from DES-Y3\, KiDS-1000\, & HSC-Y1: Table 1 from paper and Fig. 2 all panels\n\n[15: 50] Consistency of Lensing M easurements: Fig. A1\, Table A1\n\n[18:22] DarkEmulator and HOD\n\n[20:15] Joint Lensing and Clustering Fits\n\n[22: 39] Small Scale Modelling S ystematics: Fig. 4\n\n[30:10] Consistency of Clustering and GGL\n\n[30:50] Consistency of Clustering and GGL: Large Scal es: Fig. 6 left panel\n\n[32:55] Consistency of Clustering and GGL: All Scales: Fig. 6 right panel\n\n[34:18] Cosmology vs. small-scale systematics: Fig. 7\n\n[37:42] Summary\n\n[38:40] What's next?\n\n[41:58] What current cosmology work do you think is particula rly under-appreciated?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/55/ END:VEVENT BEGIN:VEVENT SUMMARY:Colin Hill\, Adrien La Posta\, and Evan McDonough (Université Par is-Saclay\, Columbia University\, University of Winnipeg) DTSTART:20220410T060000Z DTEND:20220410T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/56 DESCRIPTION:Title: The CMB's mixed messages on early dark energy... &\; the ory's response\nby Colin Hill\, Adrien La Posta\, and Evan McDonough ( Université Paris-Saclay\, Columbia University\, University of Winnipeg) a s part of Cosmology Talks\n\n\nAbstract\nColin Hill\, Adrien La Posta\, an d Evan McDonough tell us about the state of play with early dark energy (E DE). They cover both observation\, primarily the CMB\; and fundamental phy sics models that might generate EDE phenomenology.\n\nColin gives an intro to EDE\, the Hubble tension\, how the CMB is sensitive to EDE\, and EDE m odels\, and then shows how the observational evidence for/against EDE from the CMB is... curious. \n\nThe Atacama Cosmology Telescope (ACT) + large scales of Planck/WMAP appear to favour\, or even detect(!?)\, EDE at more than 3 sigma\, more or less "solving" the Hubble tension (if you ignore la rge scale structure\, which you shouldn't!). However\, the full Planck dat a sees no evidence at all\, even excluding Hubble tension solving values o f EDE at about 3 sigma. ACT+Planck also excludes EDE\, because small scale Planck is just so constraining that any ACT preference is washed out\; th ere's just so much more statistical information in Planck small scales!\n\ nAdrien then talks about how one can eliminate at least one possible CMB s ystematic via using the ratio of power spectra. When doing this there is s till a Hubble tension\, and the results are completely consistent with con ventional CMB analyses (albeit with larger error bars because some info is thrown out when taking this ratio). He then covers the same analysis as C olin's ACT analysis\, but this time with the South Pole Telescope (SPT). S PT also allows large EDE amplitudes\, but isn't constraining enough to eit her favour or rule them out.\n\nThe small additional constraining power of SPT does mean though that ACT+SPT+WMAP seems to almost conclusively detec t EDE (or some equivalent phenomena). It makes me think that *if* Planck d idn't exist\, we'd be almost convinced this is *the* answer to where the H ubble tension is coming from. Unfortunately\, Planck does exist and doesn' t see any evidence for this at all - suggesting that this is instead eithe r some systematic in ACT\, or a statistical fluke.\n\nSo\, all bets are of f\, but this is something to really keep an eye on. ACT will have much mor e data to say much more about this "within a year" (everything is blind at the moment though so nobody knows what the data will point at in the end) .\n\nFinally\, Evan talks about theory space and how one might tackle this mystery of EDE and Hubble tensions and *crucially* large scale structure. He talks about a "swampland" motivated principle that might allow the mas s of dark matter to be influenced by the early dark energy\, meaning that the "S8 tension" would not be made worse by early dark energy\, but possib ly even made better. Coupling EDE to dark matter might also help explain w hy any EDE transition happens to happen close to when the CMB is formed\, maybe... time will tell.\n\nThe talk video: https://youtu.be/T15WSiHdOFI
\n\nAdrien: https://inspirehep.net/authors/1889152
\nAdrien's paper: https://a rxiv.org/abs/2112.10754
\n\nColin: http://user.astro.columbia.edu/~jch/
\nColin's paper : https://arxiv.org/abs/2109.04 451
\n\nEvan: https ://www.evanmcdonoughphysics.com/
\nEvan's paper: https://arxiv.org/abs/2112.09128
\n\nColin 's earlier video on EDE and large scale structure: https://www.youtube.com/watch?v=5JRHFG uPAV8
\n\n
\n\nIndex to Key Parts of the Talk \n\n[0:00:0 0] Shaun's intro\n\n[0:01 :05] Colin's introductory co mments\n\n[0:02:13] Two things for people to remember from this talk\n\n[0:03:24] The background and context for this wo rk\; the Hubble Situation\n\n[0:06:01] ACT Data Release 4: significant improvement upon Planc k\, esp. on small scales\n\n[0:06:54] ACT DR4: foreground-marginalized CMB power spectra\n\n[0:08 :16] ACT DR4 Cosmology\ n\n[0:09:46] Early Dark Ene rgy: motivation - increase CMB-inferred H0\n\n[0:11:28] Importance of the FIRAS measurement\n \n[0:14:09] EDE: new compon ent - (pseudo)-scalar field\n\n[0:16:09] EDE: Parameterization\n\n[0:16:51] EDE model maintains good fit to CMB power s pectrum data with higher H0\n\n[0:17:29] LSS in EDE Model\n\n[0:18:24] EDE in Planck Primary CMB?\n\n[0:19:21] Data set combinations: Planck + BOSS (EFT) + DES/HSC/KiDS (S8)\n\n[0:20:32] Pre-ACT DR4 Summary\n\n[0:21:22] ACT DR4 EDE Analysis\n\n[0:23:53] ACT DR4 EDE Results: F ig. 1 from 2109.04451\n\n[0:27:20] Origin of ACT EDE Preference: Figs. 3\, 4 from 2109.04451\n\n [0:29:20] ACT DR4 EDE expe rimental and theoretical takeaways\n\n[0:31:53] Adrien's intro to the 2112.10754 paper (SPT-3G)\n\n[0:33:30] Two potent ial solutions on the CMB side for this tension\n\n[0:34:12] Using observables less sensitive to systematics\n\n[0:36:58] SPT-3G results vs Planck\, ACT DR4\, and SH0ES\n\n[0:39:08] Summary of EDE results\n\n[0: 39:30] New results from SP T-3G public data: Figs. 1\, 2 from 2112.10754\n\n[0:41:52] Impact of the z_c prior: Fig. 3 f rom 2112.10754\n\n[0:43:55] Combining with other CMB datasets\n\n[0:45:00] Combining with SH0ES constraint\n\n[0:46:03 ] Adrien's Conclusions \n\n[0:49:09] Evan's intro to the 2112.09128 paper\n\n[0:50:28] A recipe for the CMB: CLASS-EDE code on github\n\n[0:5 1:57] Imprint on Large Sca le Structure\n\n[0:53:38] EDE and Data\n\n[0:54:36] EDE and Theory\n\n[0:56:28] Extending the model: EDE => EDS\n\n[0:58:07] Punchline\n\n[1:00:00] Into the weeds: What drives the tigh t constraint on c?\n\n[1:02:34] The power of ACT: Fig. 10 from 2112.09128\n\n[1:04:01] The power of DES-Y3\n\n[1:0 4:40] Evan's wrap-up\n \n[1:05:50] Where to next? \n\n[1:08:10] What cur rent cosmology work do you think is particularly under-appreciated?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/56/ END:VEVENT BEGIN:VEVENT SUMMARY:Silvia Manconi (RWTH Aachen University) DTSTART:20220502T060000Z DTEND:20220502T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/57 DESCRIPTION:Title: Planck polarisation beats intensity for dark matter searche s at the galactic centre\nby Silvia Manconi (RWTH Aachen University) a s part of Cosmology Talks\n\n\nAbstract\nSilvia tells us about her recent use of Planck satellite data to search for dark matter. She doesn't use th e CMB though\, instead she is looking for microwave emission from the gala ctic centre. For her\, the CMB is noise!\n\nIf dark matter decay/annihilat ion leads to electron positron emission then those electrons and positrons would emit microwave light through synchrotron radiation as they travel t hrough the magnetic fields at the galactic centre.\n\nShe found that the p olarisation signal is a more sensitive probe of this effect than the inten sity. The main theory for why this is is that the observed signal in the p olarisation has more features (coherent hot and cold spots)\, whereas the expected dark matter signal should be more smooth. Whereas both the intens ity measurement and signal should be more smooth. Therefore\, the observed polarisation "cold spots" can best constrain the dark matter signal\, esp ecially close to the galactic centre\, where the dark matter signal should still be strong.\n\nSilvia: https://silviamanconi.wordpress.com/\n\nPaper: https://arxiv.org/abs/2204.04232\n\nRecorded Tal k: https://youtu.be/5lIPLbUyTyw \n\n
\n\nIndex to Key Parts of the Talk\n\n[00:00] Shaun's intro\n\n[00:42] Sil‎via's intro comments on this work \n\n[03:41] Two things for p eople to remember from this talk\n\n[04:43] Motivations for this work\n\n[06:55] Q&A on physics of the DM annihilation and how the synchotron intensity is relevant\n\n[11:28] What we need to model\n\n[12:19] Q&A involving Fig. S4 from the paper \n\n[14:19] Q&A involvin g Fig. S5 top panel\n\n[16:57] Getting into the details: Planck maps processing\, Fig. 1\n\n[ 21:39] Discussion on the ma gnetic fields at the galaxy center\n\n[22:59] Magnetic field models\n\n[26:16] Dark matter signal\, Fig. S3\n\n[27:2 7] Dark matter profile\, Fi g. S7\n\n[29:44] Summar y plot\, Fig. 3 right panel\n\n[34:03] Why is polarisation the most constraining?\n\n[37:32] Magnetic field configuratio n uncertainty\, Fig. 3 left panel and Fig. 8 left panel\n\n[38:24] What comes next?\n\n[39:28 ] Fig. S5 top panel\n\n [42:24] Perspectives for fo llow-up work\n\n[44:10] What current cosmology work do you think is particularly under-appreciate d?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/57/ END:VEVENT BEGIN:VEVENT SUMMARY:Andrej Dvornik and Constance Mahony (Ruhr University Bochum) DTSTART:20220617T060000Z DTEND:20220617T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/58 DESCRIPTION:Title: The Kilo-Degree Survey goes non-linear. With cosmology cons traints!\nby Andrej Dvornik and Constance Mahony (Ruhr University Boch um) as part of Cosmology Talks\n\n\nAbstract\nAndrej Dvornik and Constance Mahony tell us about the Kilo-Degree Survey (KiDS) and their progress at probing the non-linear scales with data from the survey.\n\nConstance talk s about her recent paper showing that non-linear halo bias is absolutely n ecessary if you want to avoid errors larger than 5σ on the small\, non-li near scales.\n\nAndrej takes this and does the analysis on KiDS data to ob tain cosmological constraints.\n\nConstance: INSPIRE author page\n\nConstance's paper: arxiv.org/abs/2202.01790\n\nAndrej: Personal Website\n\nAndrej's p aper: arxiv.org/abs/2210.03110< /a>\n\n
\n\nIndex to Key Parts of the Talk:
\n[00:00] Shaun's intro\n\n[00:56] Constance's overview comments on this work\n\n[01:45] Andrej's overvi ew comments\n\n[03:12] T wo things for people to remember from this talk\; start of Constance's por tion of talk\n\n[03:57] Background and context\; details on the Halo Model\; revisiting the assump tion of linear halo bias\n\n[06:05] Corrections going beyond linear-halo bias\n\n[06:47] Halo model contributions slide\; eq ns (1) in 2202.01790\n\n[07:37] Halo model power spectra\; eqns (2)\n\n[09:07] Beyond-linear halo bias\; eqn (14)\n\n[11 :03] Dark Emulator\; Appendix A of paper\n\n[11:45] Qu ick intro about KiDS\n\n[12:38] Cosmology Dependence σ8\; Fig. 1 of paper\n\n[13:58] Q&A on meaning of excess surface densi ty\n\n[15:24] Cosmology D ependence Ωm\n\n[16:02] KiDS galaxy-galaxy lensing and clustering\; Fig. 3\, main takeaway plot fr om the paper\n\n[17:52] Stellar Mass Function\; Fig. 4\n\n[18:48] HSC Y1 results with DarkEmulator+HOD (halo occupation di stribution)\n\n[19:36] C omparison to DarkEmulator+HOD\; Fig. 5\n\n[25:25] DarkEmulator+HOD Mock Analysis\; Fig. 6\n\n[ 21:03] DarkEmulator+HOD Resu lts\n\n[21:35] Constance 's Summary: Beyond-linear halo bias summary\n\n[23:11] Andrej's portion of talk: Two things for pe ople to remember\n\n[24:08] 2x2 point cosmology with SMF (stellar mass function)\n\n[25:24] Halo occupation modelling\ n\n[27:47] Describing the ga laxy bias\n\n[29:29] Fur ther assumptions in the model\n\n[31:34] Parameters\n\n[33:09] Graphic: How stellar mass correlates with the halo mass \n\n[35:08] Graphic: Stellar mass function\n\n[35:55] KiDS-1000/DR4\; The data\n\n[38:21] Measurements\n\n[40:37] Results\n\n[42:38] Comparison with other literature\n\n[47:07] Andrej's Summary\n\n[47:39] Some Q&As on where to next\n\n[53:26] What current cosmology wor k do you think is particularly under-appreciated?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/58/ END:VEVENT BEGIN:VEVENT SUMMARY:Jiamin Hou\, Zachary Slepian and Robert Cahn (U of Florida\, LBNL) DTSTART:20220819T060000Z DTEND:20220819T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/59 DESCRIPTION:Title: 7σ (!?) detection of parity violation in the large scale s tructure\nby Jiamin Hou\, Zachary Slepian and Robert Cahn (U of Florid a\, LBNL) as part of Cosmology Talks\n\n\nAbstract\nJiamin Hou\, Zachary ( Zack) Slepian and Robert (Bob) Cahn talk about their very interesting\, re cent paper looking for parity violation in the large scale structure. Cutt ing to the chase\, they find evidence for it at ~7σ. They also do various systematic tests and none reduce the significance below 4σ.\n\nTantalisi ngly\, parity violation in the LSS could be related to birefringence in th e cosmic microwave background\, with many models that would produce one\, also producing the other. Avid channel viewers will remember a talk from t wo years ago with evidence for exactly that. \n\nAre we seeing the beginni ngs of evidence for genuine parity violation on cosmological scales\, or a re the two hints caused by independent errors?\n\nThis is definitely a spa ce to watch...\n\nJiamin: https://astro.ufl.edu/directory/jiamin-hou/
\nZack: https://astro.ufl.edu/di rectory/zachary-slepian/
\nBob: http://phyweb.lbl.gov/~rncahn/www/cahn.html
\n\n Talk recording
\n\nThe paper (results): https://arxiv.org/a bs/2206.03625
\nThe paper (earlier methods): https://arxiv.org/abs/2110.12004
\n\n
\n\n< b>Index to Key Parts of the Talk\n\n[00:00] Shaun's intro\n\n[00:58] Intro comments on this work (Bob)\n\n[01:55] Two things for people to remember f rom this talk (Zack)\n\n[03:45] The background on parity violation and its applications to cosmolo gy\n\n[10:31] Cosmologic al parity violation must be from epoch of inflation\n\n[11:20] Parity violation does not conflict with homogeneity or isotropy\n\n[12:11] Parity violation with the 4PCF of LSS (Fig. 1 from 2206.03 625)\n\n[12:56] NPCFs in the Isotropic Basis\n\n[16:25] Great Find: Yutsis\, Levinson\, & Vanagas (1962)\n\n[17:63] Why is this working happening now and not earlier? (Zack)\n\n[22:26] N-Point Functions on the GPU with CADENZA\n\n[23:47] Data analysis: 2 samples us ed - BOSS DR12 LOWZ and CMASS (LRGs) (Jiamin)\n\n[24:39] Two challenges\n\n[25:14] 3 Ways We Estimate the Covariance Ma trix\n\n[28:16] Testing the Detection Significance's Robustness\n\n[29:42] Test of Analytic Covariance Matrix (Fig. 7 fr om 2206.03625)\n\n[34:38] Q&A: is it possible this is non-isotropy instead of parity violation?\n\n[37:46] Impact of Sys tematics on Parity-Odd Modes\n\n[41:18] A non-exhaustive list of potential questions\n\n[46:2 6] What are the next steps? \n\n[55:32] What curren t work in cosmology is particularly under-appreciated?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/59/ END:VEVENT BEGIN:VEVENT SUMMARY:Johannes Røsok Eskilt\, Patricia Diego-Palazuelo (U of Oslo\, U o f Cantabria) DTSTART:20220920T060000Z DTEND:20220920T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/60 DESCRIPTION:Title: 2.4σ → 3.6σ\, CMB Birefringence in 2022\nby Johanne s Røsok Eskilt\, Patricia Diego-Palazuelo (U of Oslo\, U of Cantabria) as part of Cosmology Talks\n\n\nAbstract\nJohannes Røsok Eskilt and Patrici a Diego-Palazuelo update us on the state of measurements of birefringence in the cosmic microwave background in 2022. The current most popular video on the channel was about a tentative hint of CMB birefringence back in 20 20 and much can change in two years.\n\nThe tentative hint is very much st ill present. Johannes and Patricia are both members of Planck itself and h ave spent the last few years checking for systematics\, taking the effects of EB correlations in the dust into account\, adding WMAP data\, adding a dditional frequency maps from Planck\, and checking for a frequency depend ence of the signal.\n\nSo far there are no smoking guns saying "oops\, thi s is what is causing the signal"\, so new physics is very much still on th e table.\n\nWith the additional Planck maps and WMAP data included\, as we ll as tighter modelling of the dust\, the statistical significance has dri fted up from 2.4σ two years ago to 3.6σ today\, which is exactly what on e would expect if this was a real signal.\n\nThe crucial test of this woul d be a ground based experiment like ACT\, SPT or BICEP calibrating their m isalignment angle directly with greater accuracy than Planck/WMAP can indi rectly and looking directly for an EB signal in the CMB... if they still s ee something that would be extremely interesting!\n\nRecorded talk: https://youtu.be/k9YZiWoFwzg\n\nJohan nes: ht tps://www.mn.uio.no/astro/english/people/aca/johanres/
\nPatricia: https://inspirehep.net/au thors/1954027\n\nPaper 1: h ttps://arxiv.org/abs/2201.07682
\nPaper 2: https://arxiv.org/abs/2205.13962\n\n
\n\nInde x to Key Parts of the Talk\n\n[00:00] Shaun's intro\n\n[00:49] Summary comments on this work\n\n[02:43] Two things for people to remember from this t alk\n\n[03:40] The poten tial for ground-based telescopes in this work\n\n[05:18] What is the significance of this work?\n\n[05:52] Getting into th e details\n\n[14:00] Con sistent results across 4 independent pipelines\n\n[14:31] Results\n\n[15:41] Need to correct for dust EB to obtain unbiase d measurement of birefringence\n\n[18:36] Two independent ways of mitigating the effect of dust E B\n\n[19:24] Where does dust EB come from?\n\n[21:26] Commander sky model as foreground model\n\n[22:58] What did we do next?\n\n[23:36] Q&A if there's a dust EB ampl itude prediction\n\n[25:25] What happens if we include all Planck maps?\n\n[26:24] What is the origin of the signal? (if real)\n\n[27:12] Signa l is consistent with being frequency-independent\n\n[28:28] Adding LFI increased the significance \n\n[29:28] Adding WMAP increases the significance\n\n[31:21] The fitting\; Figs. 4\,5 in 2205.13962\n\n[32:24] Miscalibration angles\; Fig. 3 in 2205.13962\n\n[33:41] Summary of Planck plus WMAP analysis\n\n[34:00] Quantifying systematics using NPIPE end-to-end simulations\n\n[39:26] FAQ\n\n[42:22] Conclusi ons\n\n[48:28] What cur rent cosmology work is particularly interesting or underappreciated?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/60/ END:VEVENT BEGIN:VEVENT SUMMARY:Richard Easther (University of Auckland) DTSTART:20221026T050000Z DTEND:20221026T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/61 DESCRIPTION:Title: The earliest gravitational structures (just after inflation )\nby Richard Easther (University of Auckland) as part of Cosmology Ta lks\n\n\nAbstract\nRichard Easther talks about the era immediately after i nflation. If reheating is delayed then the small perturbations in the dens ity of the universe grow\, just as they do during matter domination in the late universe. The growth of non-linear structures during this "early dar k age" has not been explored in depth until recently and Richard gives an overview of recent work on the topic.\n\nIt turns out that the evolution o f structures during this era is described mathematically using essentially the same equations as a fuzzy dark matter/ultralight dark matter epoch no w. This means all the tools developed for fuzzy dark matter are re-usable in this earlier epoch. In fact\, on large enough scales\, even a Newtonian N-body code suffices.\n\nThere are interesting things to explore in model s that have existed since inflation became a topic\, one doesn't need to c ook up exotic scenarios\, all that is needed is for reheating to not happe n instantly. In fact\, in units of efoldings\, this early matter dominatio n\, growth of structures period of time could even last much longer than t he late universe matter dominated phase\, meaning structures have much lon ger to grow\, and viralise\, and accrete more matter - making them a fasci nating thing to study.\n\nTalk recording: https://youtu.be/kPiCZpi1Px4\n\nRichard: https://excursionset.com/about-me\n\nPaper 1: https://arxiv.org/abs/1909.11678< /a>
\nPaper 2: https://arxiv .org/abs/1911.01661
\nPaper 3: https://arxiv.org/abs/2011.13333
\nPaper 4: https://arxiv.org/abs/2110.15109
\n\n\nIndex to Key Parts of the Talk\n\n[00:00] Shaun's intro\n\n[00:43] Richard's summary comments on this work\n\n[03: 28] Two things for people to remember from this talk\n\n[06:50] Richard's motivation for studying this early matter-dominated field\n\n[15:22] Comment s on parallels to ultralight dark matter work\n\n[18:32] Getting into the details: Post-Inflation ary Universe\n\n[19:39] Inflation Condensate\n\n[24:04] Paper 1\, 1909.11678\n\n[30:06] Self-gravitating quantum matter\n\n[33:24] Schrodinger-Poisson Equation\n\ n[35:24] Proof of Concept\n\n[38:57] Figure 2 from 1909.11678\n\n[39:18] Structure formation...\n\n[40:27] Cosmic web (simulation)\n\n[41:01] A theorist's playground\n\n[43:05] Developing/adapting new numerical tools \; 1911.01661\, 2011.1333\n\n[50:44] Simulation\, 2011.13333\n\n[51:34] Biggest smallest simulation\n\n[52:09] cf Press-Schecter\; Zoom-in simu lations\, 2110.15109\n\n[56:19] Future Work...\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/61/ END:VEVENT BEGIN:VEVENT SUMMARY:Keir Rogers (University of Toronto) DTSTART:20230122T050000Z DTEND:20230122T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/62 DESCRIPTION:Title: Ultralight dark matter and the S8 tension\nby Keir Roge rs (University of Toronto) as part of Cosmology Talks\n\n\nAbstract\nKeir tells us about constraints on the fraction of dark matter that could be "u ltralight" at various masses. \n\nIt seems probable now that one single ma ss of ultralight dark matter (ULDM) can't be responsible for all the dark matter\, but this doesn't mean it can't be a sub-component of the dark mat ter. The structure suppressing properties of ULDM could also have implicat ions for the S8 tension\, i.e. maybe a small sub-component of ULDM is what is causing the low S8 in local measurements?\n\nThe observational data Ke ir considers are the Planck CMB data and BOSS clustering data.\n\nRecorded talk\n\nKeir: keirkwame.github.io\n\nPaper: 2301.08361\n
\n\nIndex to Key Parts of the Talk\n\n[00:00] Shaun 's intro\n\n[00:53] Kier' s brief opening comments about his paper\n\n[02:38] Two things for people to remember from this tal k\n\n[04:16] What is the motivation for this research?\n\n[05:00] Find dark matter by only known interaction - gravity ( with galaxies and intergalactic gas as tracers)\n\n[05:45] Beyond the WIMP: dark matter model space \n\n[08:12] ULAs are invoked to resolve so-called CDM "small-scale crisis"\n\n[09:02] "Canonical" 10^-22 to 10^-21 eV ULA DM is ruled out\n\n[09:37] Stri ngy axions & the string axiverse\n\n[13:08] Multi-probe approach to detect ULAs\n\n[15:25] Axions are dark matter and dark e nergy candidates\n\n[17:13] Simulation animations with and without axions\n\n[19:08] S8 tension\n\n[22:46] ULA DM causes scale-dependent suppressi on in matter clustering\n\n[26:45] Axions lower S8\n\n[27:50] Lightest axions constrained by CMB\n\n[30:01] Planck 2018 reionisation bump breaks a xion degeneracies\n\n[32:16] DM-like axions lower S8\; DE-like axions lower h\n\n[33:54] High-resolution CMB marginally we akens axion constraint\n\n[40:01] Model galaxy clustering into mildly non-linear regime with EFT o f LSS\n\n[42:34] Galaxy clustering traces DM clustering - revealing signature of ULAs\n\n[44:0 5] BOSS DR12 galaxy clusteri ng rules out new parts of axion parameter space\n\n[45:50] Axions improve consistency between Plan ck and BOSS\n\n[47:49] B OSS has mild preference at m_a = 10^-26 eV - excluded by Planck\n\n[53 :17] Strongest axion bounds come from combining CMB & LSS\n\n[54:29] Window of DM-like axions with lower S8\n\n[54:56] Could axions resolve the S8 ten sion\n\n[55:55] Multi-pr obe approach to detect ULAs\n\n[1:00:15] Where to next?\n\n[1:03:35] What current work in cosmology is particularly undera ppreciated by the community?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/62/ END:VEVENT BEGIN:VEVENT SUMMARY:Johannes Lange (Leinweber Center for Theoretical Physics\, Univers ity of Michigan) DTSTART:20230205T050000Z DTEND:20230205T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/63 DESCRIPTION:Title: S8 constraints from (very) non-linear scales in combined DE S\, KiDS & BOSS\nby Johannes Lange (Leinweber Center for Theoretical P hysics\, University of Michigan) as part of Cosmology Talks\n\n\nAbstract\ nJohannes Lange tells us about his recent work with collaborators constrai ning cosmological parameters\, in particular S8\, using the non-linear sca les in the Dark Energy Survey (DES)\, the Kilo Degree Survey (KiDS) and th e Baryon Oscillation Spectroscopic Survey (BOSS).\n\nThey generate predict ions for the non-linear scales via the Aemulus suite of simulations\, whic h ran with a variety of cosmological parameters. To connect the simulation s' halos with galaxy observations they use a halo occupation distribution (HOD) model to generate a large number of sets of mock galaxies. The halo model parameters are then marginalised over when comparing the mocks to ob servations\, ultimately giving the final cosmology constraints.\n\nAs with more or less all other large scale structure probes nowadays they find a mild tension between their constraints and predictions for S8 coming from CMB observations and the LCDM model.\n\nTalk recording: youtu.be/XxCIpFMP_lw\n\nJohannes' web site: johannesulf.github.io/\n\nPaper: < a href="https://arxiv.org/abs/2301.08692">arxiv.org/abs/2301.08692\n\n halotools code: github.com/ astropy/halotools\n\ndsigma code: github.com/johannesulf/dsigma\n\n
\n\nIndex to Key P arts of the Talk\n\n[00:00] Shaun's intro\n\n[01:16] Johannes' brief opening comments about the paper\n\n[03:45] Two things for people to remember from this talk\n\n[05:43] Wha t are the motivations for this work?\n\n[08:26] Several advancements in recent years made this work possible\n\n[09:12] Halo tools\, by Andrew Hearin\n\n[09:26] Multi-Cosmology Simulations\n\n[10:04] "lensing is low"\n\n[13:36] Getting into the details: Galaxy Redshift-Spac e Clustering\n\n[15:12] G alaxy-Galaxy Lensing (dsignma python package\, by Johannes)\n\n[17:54] Comparing galaxy-galaxy len sing measurements in this work vs older measurements\n\n[20:18] Projected Clustering + Lensing \n\n[22:24] Mock Galaxy Cata logs\n\n[22:41] Multi-Co smology Simulations -> Aemulus\n\n[24:09] HOD (Halo Occupation Distribution) Model\n\n[25:36] Assembly Bias\n\n[26:22] Velocity and Spatial Bias\n\n[28:20] Cosmological C onstraints\; Cosmology Inference\n\n[32:33] Mock Test\; Figure 2 from paper\n\n[34:48] Blinding\; Figure 5\n\n[35:58] Data fits\; Figure 6\n\n [38:54] S8 Constraints plot\ ; Figure 12 (key slide)\n\n[41:47] Where to next? Future Directions\n\n[43:15] SZ Cross-Correlation\n\n[43:50] Baryonic Feedback\n\n[44:58] DESI\, successor to BOSS (expe ct much better constraints)\n\n[45:42] More tests on mock catalog\n\n[46:23] Speculative question: pretend the S8 tension is systematics\, what might be the leading reason for it?\n\n[47:59] < a href="https://youtu.be/XxCIpFMP_lw?t=2879">What current work in cosmolog y is particularly underappreciated by the community?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/63/ END:VEVENT BEGIN:VEVENT SUMMARY:Stuart Lyall (Swinburne University) DTSTART:20230302T050000Z DTEND:20230302T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/64 DESCRIPTION:Title: Peculiar velocities will detect or constrain modified gravi ty (e.g. f(R) & DGP)\nby Stuart Lyall (Swinburne University) as part o f Cosmology Talks\n\n\nAbstract\nStuart tells us about his recent work exp loring how to use peculiar velocity measurements to constrain modified gra vity (specifically f(R) and DGP models). He finds that even using just lin ear scales we would be able to detect or rule out model parameter regions that would be entirely consist with current measurements of the background expansion.\n\nHe does this by predicting the auto and cross spectra betwe en galaxy overdensity and peculiar velocity\, using just linear theory - a nd then analysing those observables in modified gravity simulations to mea sure the parameters used in the simulations.\n\nAt this point it is just a proof of concept\, as for each modified gravity scenario the method is on ly constraining the linear galaxy bias and one model parameter (other cosm ological parameters are known) and also not taking into account additional observational uncertainties involved in measuring peculiar velocities in the real world.\n\nStill\, the method does work\, at least when the effect produces a large enough deviation from LCDM so the proof of concept works . Future careful work with 6DF and SDSS data (and\, one day soon\, DESI) s hould allow the method to bring about real constraints on these models.\n\ nRecorded talk\n\nPaper: arxiv.org/abs/2211.07101\n\n
\ n\nIndex to Key Parts of the Talk \n\n[00:00] Introductory comments by Shaun and Stuart\n\n[0 1:35] Two things you would lik e people to remember from this talk\n\n[02:20] What is Dark Energy?\n\n[03:38] Literature review\n\n[04:15] Peculiar Velocity\n\n[07:15] Growth of Structure\n\n[09:35] Pipeline Overview\n\n[11:43 ] Modified Gravity Models \n\n[15:31] Simulation Data\n\n[16:05] Correlation Fun ctions\n\n[17:16] Theore tical Correlation Functions\n\n[21:52] χ² Fitting\; Figure 3 from paper\n\n[22:38] Results\; Figures 7 and 9\n\n[27: 20] Fisher Forecasts\; Figur es 11 and 12\n\n[29:52] Apply to Real Surveys\; comments on main purpose of this work\n\n[31:5 1] Preliminary Real Results< /a>\n\n[34:29] Where to next ? and Investigating Environmental Dependence\n\n[36:48] What current work in cosmology is particul arly underappreciated by the community?\n
\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/64/ END:VEVENT BEGIN:VEVENT SUMMARY:Minh Nguyen (University of Michigan) DTSTART:20230311T050000Z DTEND:20230311T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/65 DESCRIPTION:Title: 3.7 sigma evidence for suppression of growth of structure! (and S_8 resolved?)\nby Minh Nguyen (University of Michigan) as part o f Cosmology Talks\n\n\nAbstract\nMinh Nguyen tells us about his recent wor k looking for evidence of modified gravity in cosmological observations. R ather than look at a specific model\, Minh and his collaborators look for evidence of a deviation in the "growth index" γ.\n\nIn general relativity and ΛCDM γ≃0.55 but in a more general theory of gravity it could devi ate. Minh looks at measurements of peculiar velocity\, clustering and Plan ck CMB data (temperature\, polarisation and lensing) and finds 3.7σ evide nce for γ greater than 0.55.\n\nThis is not perhaps surprising\, as it ti es in with the S₈ tension. γ quantifies how fast structure grows in th e universe and where we already know there is a deficit of structure in th e late universe. Moreover γ greater than 0.55 would cause a deficit. \n\n However\, it is still impressive that this one parameter is able to provid e a good fit to the various data sets simultaneously. This doesn't look li ke a "resolution" that takes CMB and late universe probes into bad fitting regions of parameter space. In fact\, Planck CMB alone even has weak evid ence for γ greater than 0.55 because it appears to also help with the A_l ens tension.\n\nA fascinating development to keep an eye on...\n\nTalk recording\n\nPaper: arxiv.org/abs/2302.01331\n\nMinh: minhmpa.github.io\n\nCode: github.com/MinhMPA/CAMB_Gam maPrime_Growth\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/65/ END:VEVENT BEGIN:VEVENT SUMMARY:Giovanni Arico (University of Zurich) DTSTART:20230410T060000Z DTEND:20230410T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/66 DESCRIPTION:Title: Cosmology Without Scale Cuts! (DES Cosmic Shear Baryonified )\nby Giovanni Arico (University of Zurich) as part of Cosmology Talks \n\n\nAbstract\nGiovanni Arico tells us about his recent work adding baryo ns to the modelling of Dark Energy Survey cosmic shear analysis. By adding baryonic modelling he and collaborators are able to use all of the DES da ta. \n\nThe cosmological constraints don't tighten a lot\, because althoug h a lot of data is added\, the baryonic effects are largely degenerate wit h cosmology. However\, they are able to obtain a clear lower bound on one of the baryonic parameters\, which parameterises the typical halo mass tha t has ejected 50% of its gas.\n\nTheir results are 1.4σ different the DES ' own cosmic shear analysis\, and therefore their S₈ measurement is not in tension with Planck. This isn't mainly due top the baryons though\, so there is no clear story that "baryons are responsible for the S₈ tension ". Instead the difference comes roughly half from the methods to include n on-linear clustering and half from intrinsic alignment modelling.\n\nThis isn't a death knell for the S₈ tension in any case because DES cosmic sh ear alone wasn't in very large tension with Planck\, and many other measur ements are - however it does highlight how a number of assumptions\, each on their own small enough to perhaps not worry about\, can ultimately add up to something more substantial.\n\nThe future is bright as\, with approp riate modelling\, the "baryonification" methods used here can be used for all the other large scale structure measurements out there. Also\, if the baryon parameters are constrained with additional data sets (tSZ\, kSZ\, X -ray temperature\, stellar mass function\, etc) then the degeneracies with cosmological parameters can be broken\, allowing full constraining power from these small scales.\n\nTalk re cording\n\nGiovanni: linkedin.com/in/giovanni-aricò-8832684a\n\nPaper: arxiv.org/abs/2303.05537\n\nBAC COemu: bitbuc ket.org/rangulo/baccoemu/src/master/\n\n
\n\nIndex to Key Parts of the Talk\n\n[00:00] Int roductory comments by Shaun\n\n[01:38] Giovanni's opening comments on the paper\n\n[02:32] Two things for people to remember from this talk\n\n[03:58] What motivated this work?\n\n[05:14] Discussion about the scale cuts\, baryonification process\, e tc\n\n[08:46] Getting int o the details\n\n[11:11] Model: BACCO framework\n\n[16:16] BACCOemu\n\n[18:57] Pipeline: Bayesian inference (Table I in paper\, free parameters) \n\n[22:48] Results: Cosmolo gy (Figure 3)\n\n[26:21] Results: Baryons (Figure 4)\n\n[29:53] Results: Intrinsic Alignment\n\n[31:30] Intrinsic alignment of galaxies: NLA prefe rred over TATT\n\n[32:28] S8 tension (Figs. 6\, 7)\n\n[36:00] S8 tension (Figure 8)\n\n[40:49] Difference with DES Collaboration (Figure 10)\n \n[49:07] Q&A on this work i n relation to KiDS\n\n[54:16] Where to next?\n\n[56:32] What current work in cosmology is particularly underappreciated by the community?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/66/ END:VEVENT BEGIN:VEVENT SUMMARY:Jeongin Moon\, David Valcin\, Christoph Saulder (Sejong U\, Ohio U \, Max Planck Inst) DTSTART:20230513T060000Z DTEND:20230513T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/67 DESCRIPTION:Title: Actual DESI Results! - BAO with BOSS Precision after just t wo months\nby Jeongin Moon\, David Valcin\, Christoph Saulder (Sejong U\, Ohio U\, Max Planck Inst) as part of Cosmology Talks\n\n\nAbstract\nJe ongin Moon\, David Valcin and Christoph Saulder tell us about the first co smologically relevant results from DESI (The Dark Energy Spectroscopic Ins trument). Specifically\, they are presenting the first detection of the BA O (Baryon Acoustic Oscillations) from DESI.\n\nWith a "first detection" on e would expect something mediocre\, but even this result\, using only two months of DESI data\, has similar precision to the final BOSS data after y ears of operation. This is a very exciting time for cosmology as we wait f or the full one year DESI results and cosmological constraints.\n\nJeongin \, David and Christoph talk us through the galaxy subsets DESI will use (a nd which they have used in this analysis) as well as the statistical signi ficance of the BAO detection and modelling required to quantify this.\n\nW ith this detection they are able to also provide a forecast for the one ye ar and five year results that is actually data driven\, based on what they 've actually seen so far (rather than just optimistic modelling). The fore cast for the five year measurement looks exquisite.\n\nJeongin: arxiv.org/search/astro-ph?q...\n\nDavid: inspirehep.net/authors/1887016\n\nChristoph: cosmology.kas i.re.kr/members.php?member=saulder\n\nPaper: 2304.08427\n\n
\n\n[00:00] Intro comments\n\n[01:01] When can we expect the year 1 data analysis?\n\n [01:28] Two things for people to remember from this talk\n\n[02:19] What are Baryon Acoustic Oscillations?\n\n[04:16] Why are Baryon Acoustic Oscillations Useful?\n\n[05:45] BAO R econstruction\n\n[09:24] Plan for DESI\n\n[10:42] The Instrument (and comparison with SDSS)\n\n[12:55] Main tracers of DESI\n\n[16:50] DESI will explore a x30 larger map ove r a x10 larger volume than SDSS\n\n[18:17] Our work with early DESI data\n\n[18:52] First two months of observations\n \n[19:34] Correlation functi on measurements\n\n[21:40] Simulations and the covariance matrix\n\n[27:10] Detection in simulations\n\n[30:11] BAO reconstruction efficiency\ n\n[31:20] BAO detection usi ng LRG and BGS\n\n[33:23] Correlation function measurements\n\n[34:18] Fisher forecast\n\n[35:28] Summary\n\n[37:03] Outlook\n\n[38:21] What current work in cosmology is particularly underapprec iated by the community?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/67/ END:VEVENT BEGIN:VEVENT SUMMARY:Dongwon Han\, Niall MacCrann\, Mathew Madhavacheril\, Frank Qu\, Blake Sherwin (U of Cambridge\, U of Pennsylvania) DTSTART:20230525T060000Z DTEND:20230525T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/68 DESCRIPTION:Title: Advanced ACT Lensing Cosmology (the best high redshift\, la rge scale take on the S8 tension)\nby Dongwon Han\, Niall MacCrann\, Mathew Madhavacheril\, Frank Qu\, Blake Sherwin (U of Cambridge\, U of Pen nsylvania) as part of Cosmology Talks\n\n\nAbstract\nDongwon Han\, Niall MacCrann\, Mathew Madhavacheril\, Frank Qu\, and Blake Sherwin tell us abo ut the Atacama Cosmology Telescope's latest measurement of CMB weak lensin g ("Advanced ACT" to be precise).\n\nIt is quite the measurement. Despite ACT being on the ground\, the measurement now rivals the best Planck lensi ng measurement. This means the additional complications of the atmosphere have been overcome\, and the better technology of telescope possible from not having to put something in space are starting to win.\n\nThe results a re fascinating in the era of S₈ tensions. They match both Planck CMB and Planck lensing (and ACT primary CMB). The CMB lensing measurements are se nsitive to larger scales and higher redshifts than other large scale struc ture probes (because the CMB is further away\, so is lensed by stuff furth er away). This means that if the S₈ tension is new physics their result seems to be suggesting it must happen at late times and/or on small scales . Perhaps this is consistent with what other probes are suggesting too?\n\ nIn this video we hear about the hard work done to eliminate systematic ef fects and make sure noise isn't being mistaken for signal\, and then we he ar about the cosmology results and their implications for the future.\n\nP aper 1: arxiv.org/abs/2304.0520 3
\nPaper 2: arxiv.org/a bs/2304.05202
\nPaper 3: arxiv.org/abs/2304.05196
\n\nDongwon: dwhan89.github.io
\nNiall: maths.cam.ac.uk/person/nm746
\nMathew: upenn.edu/people/mathew-madhavacheril
\nFrank: linkedin.com/in/frankqu7
\nBlake: < a href="http://www.damtp.cam.ac.uk/person/bds30">damtp.cam.ac.uk/person/bd s30\n\n[00:00] Intro bits
\n[02:50] Why is this important now?
\n[14:32] ACT and its maps
\n[18:35] ACT lensing maps
\n[27:56] The power spectrum from t he map (and challenges!)
\n[40:54] Cosmology Results! (and implications)< /a>
\n[1:01:39] What comes next (and discussion)
\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/68/ END:VEVENT BEGIN:VEVENT SUMMARY:Alexandra Amon\, Ami Choi\, Anna Porredon\, Catherine Heymans\, Ma rika Asgari\, Simon Samuroff (DES\, KiDS) DTSTART:20230529T060000Z DTEND:20230529T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/69 DESCRIPTION:Title: DES & KiDS Combined Cosmology Constraints (No Tension with Planck?!)\nby Alexandra Amon\, Ami Choi\, Anna Porredon\, Catherine He ymans\, Marika Asgari\, Simon Samuroff (DES\, KiDS) as part of Cosmology T alks\n\n\nAbstract\nMembers from the Dark Energy Survey and Kilo Degree Su rvey have teamed up to do a joint cosmic shear analysis\, complete with fi nal cosmology results. They tell us the final cosmology results\, and go i nto details explaining what the technical difficulties were to combine the data sets.\n\nTalk Recording: yout u.be/T8hkgJ-hFoo\n\nTalk Slides: https://docs.goog le.com/presentation...\n\nPaper: arxiv.org/abs/2305.17173\n\nAlexandra Amon: alexandraamon.com\n\nAmi Choi: amichoi.github.io\n\nAnna Porredon: ph.ed.ac.uk/...\n\nCatherine Heyma ns: roe.ac.uk/~heymans\n\nMa rika Asgari: hull.ac.uk/...\n\nSimon Samuroff: inspirehep.net/...\n\nDES: darkenergysurvey.org/...\n\nKiDS: kids.strw.leidenuniv.nl/......\n\nHSC: hsc-release.mtk.na o.ac.jp/...\n\n
\n\n[00:00] Shaun's intro\n\n[01:13] Opening comments on the work\; Fig. 7 from the paper\n\n[05:28] < a href="https://youtu.be/T8hkgJ-hFoo?t=328s">The results: KiDS + DES cosmi c shear\; Fig. 1\n\n[09:51] When can we expect KiDS + DES 3x2pt analysis?\n\n[11:19] Two takeways for people to remember f rom this talk\n\n[12:06] Background on the cosmic shear surveys\n\n[13:52] Cosmology from cosmic shear in 2023\n\n[16: 20] Overview of the process going from input images to output cosmological parameters\n\n[21:15] < a href="https://youtu.be/T8hkgJ-hFoo?t=1275s">Analysis choices matter! \n\n[30:04] Choices made be tween various possible analysis methods\; Mock analysis\; Hybrid pipeline< /a>\n\n[36:53] Re-analysis of KiDS-1000 and DES Y3\n\n[42:07] Re-analysis of HSC Y3\n\n[43:52] The combination of the two surveys\n\n[46:27] The S8 tension\n\n[49:40] Analysis variants\n\n[ 52:14:] Accounting for nonl inear growth and baryonic feedback\n\n[56:05] Looking ahead\n\n[59:58] What current work in cosmology is particularly und erappreciated by the community?\n\n[1:00:56] Comments from Catherine Heymans\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/69/ END:VEVENT BEGIN:VEVENT SUMMARY:Jenny Wagner DTSTART:20230625T060000Z DTEND:20230625T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/70 DESCRIPTION:Title: The Case Against the Cosmological Principle (and/or FLRW)\nby Jenny Wagner as part of Cosmology Talks\n\n\nAbstract\nJenny Wagner gives us the observational case for and against the Cosmological Principl e\, based on a paper she and 22 co-authors wrote summarising this case. \n \nShe starts by clearly defining what the Cosmological Principle is and th en talks us through the observations that she and her coauthors find to be the most compelling evidence against the assumptions of full statistical isotropy and homogeneity. In each case she gives us the story either "side " would need to tell to reconcile the observation (the standard\, FLRW sid e and the inhomogeneous cosmology side).\n\nJenny: thegravitygrinch.blogspot.com\n\nRecording: https://youtu.be/nASUsWQyemc\n\ nPaper: arXiv: 2207.05765\n \n
\n\n[00:00] Intro and take home messages\n\n[07:27] Background and motivation\n\n[12:40] What is the Cosmological Principle?\n\n[20:50] Half sky analyses of the CMB\n\n[30:19] 'Scale of homog eneity'\n\n[38:09] Variations in time and space of cosmological parameters\n\n [51:05] Elli s-Baldwin and anomalous dipoles\n\n[1:01:47] What comes next?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/70/ END:VEVENT BEGIN:VEVENT SUMMARY:Lilan Yang\, Mike Boylan-Kolchin (Kavli IPMU\, U of Texas) DTSTART:20230716T060000Z DTEND:20230716T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/71 DESCRIPTION:Title: Too Big\, Too Early? (High Redshift JWST Galaxies)\nby Lilan Yang\, Mike Boylan-Kolchin (Kavli IPMU\, U of Texas) as part of Cosm ology Talks\n\n\nAbstract\nLilan Yang and Mike Boylan-Kolchin tell us abou t high redshift JWST galaxies. Lilan is one of the astronomers using JWST to look at high redshifts and find new galaxies. Mike is a cosmologist who has pioneered looking at these high redshift galaxies to think about cosm ology.\n\nRecording: https://youtu. be/ApB4Jv3P9Gs\n\nPapers: 2 207.13101\, 2207.13527\ , 2208.01611\, 2212.06666\n\n00:00 Shaun's Intro\n\n01:19 Lilan intro to JWST\n\n05:40 L ilan: What are the first stars and galaxies?\n\n13:02 Lilan: How did reionization o ccur?\n\n28:03 Mike: Are observed structures consistent with initial conditions?\n\n47:01 Mike: Physics beyond ΛCDM\n\n1:00:03 Lilan and Mike: Summary and what's next? \n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/71/ END:VEVENT BEGIN:VEVENT SUMMARY:Cyril Creque-Sarbinowski (Center for Computational Astrophysics\, Flatiron Institute) DTSTART:20230827T060000Z DTEND:20230827T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/72 DESCRIPTION:Title: Parity Violation from Inflation (via Chern-Simons Gravity)< /a>\nby Cyril Creque-Sarbinowski (Center for Computational Astrophysics\, Flatiron Institute) as part of Cosmology Talks\n\n\nAbstract\nCyril Creque -Sarbinowski tells us about recent work on Chern-Simons gravity and how if it is the correct general model of gravity then parity violation can be g enerated during inflation in such a way that correlation functions of gala xies measured today could see that parity violation. Given the recent evid ence for parity violation in galaxy correlation functions\, that is intrig uing.\n\nThe model also requires parameter values that could produce baryo genesis\, so the same physics would end up producing the (observed?) parit y violation and the baryon asymmetry in the universe.\n\nEven if the curre nt hints of parity violation turn out to be wrong\, future experiments wou ld be sensitive to smaller magnitudes of this effect\, meaning the model w ill be well constrained by the next wave of large scale structure measurem ents\n\nCyril: cyril-creque.gith ub.io\n\nPaper: arxiv.org/a bs/2303.04815\n\n
\n\n[00:00] Sean's intro\n\n[00:47] Cyril's brief intro on the paper\n\n[01:46] Two things to remember from this talk\n\n[02:17 ] The motivation for this wor k\n\n[03:15] What is Pari ty? How can Gravity violate it?\n\n[05:25] What is [dynamical] Chern-Simons (dCS) Gravity?\n\n[ 07:33] How can Parity be Obse rved? (Galaxy N-Point Functions)\n\n[09:02] The Galaxy Four Point Function / Trispectrum\n\n[11 :53] Inflation: A Lightning R eview\n\n[14:43] dCS Infl ation: Full Action\n\n[18:58] Primordial Scalar Trispectrum from dCS\n\n[23:55] The Collapsed Limit\n\n[24:24] The Collapsed Limit Scalar Trispect ra\n\n[31:21] Two Exampl es Beyond Vanilla dCS Inflation\n\n[35:37] How Sensitive are we to Collapsed Trispectra?\n\n[4 4:05] What about Experiments ?\n\n[46:17] dCS Inflati on: Lepto/Baryogenesis\n\n[53:35] Conclusions / Future Extensions\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/72/ END:VEVENT BEGIN:VEVENT SUMMARY:Gerrit Farren\, Alex Krolewski (Cambridge\, Perimeter Institute) DTSTART:20230911T060000Z DTEND:20230911T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/73 DESCRIPTION:Title: S8 at low redshift and large scales - ACT lensing X unWISE galaxies\nby Gerrit Farren\, Alex Krolewski (Cambridge\, Perimeter Ins titute) as part of Cosmology Talks\n\n\nAbstract\nGerrit Farren and Alex K rolewski tell us about their work cross correlating the ACT lensing maps w ith unWISE galaxies. Their method is an update of earlier analyses using P lanck lensing. Those earlier analyses were in tension with Planck primary CMB measurements\, which was similar to e.g. cosmic shear\, and other clus tering measurements\, at smaller scales.\n\nCuriously\, this new analysis reveals no tension with primary CMB. A re-analysis of Planck lensing cross unWISE\, with updated assumptions and modelling\, shows that Planck lensi ng is actually also not in tension with primary CMB (a combination of effe cts were responsible for removing the tension).\n\nThis analysis covers th e large(ish) scale low(ish) redshift quadrant of the (k\,z) space\, sugges ting that the origin of the S8 tension is likely to either be a very low r edshift phenomenon\, or scale dependent.\n\nHowever Alex and Gerrit do not e that a recent cross-correlation of Planck with DESI LRGs does seem to st ill indicate some tension at the same redshift and scales\, so the dust ha sn't 100% settled on the large scale\, low redshift quadrant.\n\nVideo rec ording: youtu.be/Y_QMPWDi95s\n\ nGerrit: maths.cam.ac.u k/person/gsf29\n\nAlex: perimeterinstitute.ca/people/alex-krolewski\n\nPaper: arXiv: 2309.05659\n\n
\n [00:00] Shaun's intro\n\n[ 01:06] Overview comments by Ge rrit and Alex\n\n[03:31] Two things to remember from this talk\n\n[04:40] Motivations for this work\n\n[07:41] Measuring S8 with galaxy-CMB lensing c ross-correlations\n\n[09:16] New ACT DR6 X unWISE spectra (Fig. 3 from paper)\n\n[12:03] Q&A: Advantages of using UnWISE vs eBOSS in this work\n\n[13:13] Background: defining the unWISE sample\n\n[18:21] Background: previous unWISE-Planck results< /a>\n\n[19:08] Clustering re dshifts for unWISE\n\n[21:00] Improving the galaxy sample: updated redshift distribution\n\n[2 2:24] Mitigating systematic density fluctuations\n\n[25:59] Modelling improvements: Redshift marginalisation (Fig. 17)\n\n [27:45] Modelling improvemen ts: The power spectrum model\n\n[29:36] Series of systematics tests: Data null-tests\n\n[31:06 ] Series of systematics test s: Simulation driven tests (Fig. 12)\n\n[31:58] Series of systematics tests: Parameter consistency tests (Fig. 21)\n\n[32:28] Cosmology from ACT DR6 Lensing X unWISE (Fig. 19)\n\n[35:33] Reanalysing Planck Lensing X unWI SE: MC norm correction\n\n[36:47] Reanalysing Planck Lensing X unWISE: Planck PR4 lensing\n\n[ 37:16] Reanalysing Planck Le nsing X unWISE: summary of changes\n\n[38:12] Reanalysing Planck Lensing X unWISE: Cosmology\n \n[40:22] Joint constraints from ACT DR6 and Planck PR4 X unWISE (Fig. 23)\n\n[41:12] Comparing to other analyses (Fig. 23)\n\n[45:09] Future CMB lens ing cross-correlations\n\n[50:51] What current work in cosmology is particularly underappreciated by the community?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/73/ END:VEVENT BEGIN:VEVENT SUMMARY:Melissa Diamond\, Chris Cappiello (Queens U.) DTSTART:20231003T050000Z DTEND:20231003T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/74 DESCRIPTION:Title: If Dark Matter Interacts with Protons We Could See It Scatt er Electrons\nby Melissa Diamond\, Chris Cappiello (Queens U.) as part of Cosmology Talks\n\n\nAbstract\nMelissa Diamond\, joined by Chris Cappi ello\, tells us how dark matter interactions with one set of standard mode l particles might be first constrained via experiments looking for interac tions with other particles.\n\nAs a first example they explore how loop di agrams that arise when dark matter interacts with quarks (and thus pions\, neutrons and protons)\, necessarily introduce an interaction with electro ns too. For light enough dark matter\, this would mean that the first dire ct detection of these dark matter models would come via electron scatterin g experiments\, not nucleon scattering experiments.\n\nAt the moment this just adds to constraints in somewhat less-interesting parameter space\, bu t future experiments will push the constraints into well motivated paramet er ranges for dark matter production mechanisms.\n\nThis loop interaction would also generate a dark matter "millicharge"\, which could be combined with astrophysical observations to make even tighter constraints.\n\nTalk recording: youtu.be/gixAFpnVhAw \n\nPaper: arXiv: 2307.13727\n\nMelissa: inspirehep. net/authors/1945406\n\nChris: mcdonaldinstitute.ca/chris-cappiello\n\n
\n\nIndex to Key Parts of the Talk\n\n[00:00] Shaun's intro\n\n[00:56] Overview comments by Melissa\n\n[01:39] Two things to remember from this talk< /a>\n\n[02:31] Motivations fo r this work\n\n[04:48] Ex planation of Figure 1 from paper\n\n[06:20] Why should there be an interaction of DM with the SM?\n\n[08:04] More specific m otivation\n\n[09:35] Chri s on SENSEI and DAMIC\n\n[12:24] Explanation of the blue Cosmology line on the plot\n\n[13:20] Getting into the details (Fig s. 2\, 7)\n\n[20:41] Chi ral Effective Interaction\n\n[26:44] Calculating the Cross Sections\n\n[30:50] Effective Electron Cross Section\n\n[32 :25] Probe Hadrophilic DM wi th a Heavy Mediator using Electron Coil Detectors\n\n[35:15] Bounds from Effective Millicharge \n\n[44:48] Where to next?\n\n[52:12] What current w ork in cosmology is particularly underappreciated by the community?\n\ n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/74/ END:VEVENT BEGIN:VEVENT SUMMARY:Kate Clements (University of Nottingham) DTSTART:20231103T050000Z DTEND:20231103T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/75 DESCRIPTION:Title: A Lab Experiment to Detect Dark Sector Domain Wall\nby Kate Clements (University of Nottingham) as part of Cosmology Talks\n\n\nA bstract\nKate tells us about her recent work showing how domain walls in t he dark sector could be trapped in a laboratory. \n\nIn many well motivate d models\, a scalar field in the dark sector can have a double well potent ial. In this case\, the scalar field can form "domain walls" if in some re gion of space the field occupies one side of the well\, and in other regio ns of space the field occupies the other side of the well. The wall occurs at the transition point between the two regions.\n\nNormally such domain walls will not stick around\, either evaporating\, or simply moving away f rom an observer. However\, by putting a density spike in a vacuum chamber one can trap a domain wall in place. Once trapped\, one could observe the domain wall's effects on standard model particles\, e.g. cold atoms\, via a change in a fifth force.\n\nOf all the ways we're looking for new fundam ental physics\, this sort of experiment would be the coolest if it worked\ , as it would be reproducible in labs around the world\, making experiment al fundamental physics cheap (ish) again.\n\nPaper: arXiv:2308.01179\n\nTalk Video: youtu.be/U6arawZnxHQ\n\nKate: linkedin.com: Kate Clements\n\n
\n\nIndex to Key Parts of the Talk
\n[00:00] Shaun's intro\n\n[00:39] < a href="https://youtu.be/U6arawZnxHQ?t=39s">Overview comments by Kate\ n\n[01:21] Two things to reme mber from this talk\n\n[02:07] Motivations for this work (Fig. 1 from the paper)\n\n[04:42] Detecting Dark Domain Walls\n\n[05:57] What is a Domai n Wall?\n\n[08:45] Infin ite Domain Walls\n\n[09:37] Vacuum Chamber Experiment\n\n[12:49] Thin Domain Walls (Fig. 2)\n\n[14:41] Thick Domain Walls (Fig. 3)\n\n[16:00] What Next?\n\n[24:48] What current work in cosmolog y is particularly underappreciated by the community?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/75/ END:VEVENT BEGIN:VEVENT SUMMARY:Keir Rogers\, Vivian Poulin (U Toronto\, U Montpellier) DTSTART:20231201T050000Z DTEND:20231201T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/76 DESCRIPTION:Title: 4.9σ evidence for axions & warm dark matter - eBOSS Lyα v s Planck CMB\nby Keir Rogers\, Vivian Poulin (U Toronto\, U Montpellie r) as part of Cosmology Talks\n\n\nAbstract\nKeir and Vivian tell us about their recent work looking at the Lyman-α power spectrum from eBOSS quasa rs. Specifically\, they look at how consistent this power spectrum is with the power spectrum one would expect from the relevant scales given Planck CMB observations within the ΛCDM model and find a whopping 4.9σ tension .\n\nThere have been hints of a tension between Lyman-α and CMB for a whi le\, but not with this magnitude. Keir and Vivian focus their analysis on the scales and observables that the eBOSS Lyman-α are most sensitive to a nd see that the slope of the power spectrum of this range of scales is ver y different to what is seen on CMB scales. Within ΛCDM the slope of the p ower spectrum should be constant\, hence the whopping tension.\n\nMost exc itingly\, they also find three simple models that more or less completely solve the tension\, without harming any other observations! These are a on e-parameter power-law running of the "spectral index" (i.e. the slope of t he power spectrum)\, and a small fraction of axion "ultralight" dark matte r\, or warm dark matter. For the axion and warm dark matter models there a re two free parameters (the mass and the fraction of the total dark matter ). The running and axion models in particular completely remove the tensio n\, and the warm dark matter reduces the "tension" to 1.5σ. Very exciting !\n\nVideo Recording: youtu.be/_cue UDEf6n4\n\nKeir: keirkwame.gith ub.io/\n\nVivian: ins pire.net/authors/1341720\n\nPaper: arXiv: 2311.16377\n\n
\n\nIndex to Key Parts of the Talk\n[00:00] Shaun' s intro\n\n[01:04] Overvi ew comments by Keir and Viv\n\n[03:25] Two things to remember from this talk\n\n[06:45] Motivations for this work\n\n[ 11:35] Getting into the Deta ils\n\n[15:57] All the c osmological info in the eBOSS Lyα forest compressed to two parameters \n\n[17:20] This compressio n is valid for all the models we consider (Fig. 4 from paper)\n\n[18:2 6] 4.9σ tension between eB OSS Ly-αf & Planck CMB (Fig. 1)\n\n[20:11] Clarifying comments by Shaun (editing insert)\n\n [23:27] CMB+BAO+SNe vs Lyα \; power spectrum running\, ULA\, WDM (Fig. 2 top)\n\n[34:40] Tension missed when looking at omeg a_8\, n_s (Fig. 2 bottom\n\n[36:35] Planck CMB+BAO+SNe+eBOSS Ly-αf constraints on primordial pow er spectrum (Fig. 3)\n\n[37:39] Planck CMB+BAO+SNe+eBOSS Ly-αf constraints on nature of dark mat ter (Fig. 3)\n\n[39:25] What else may be causing this discrepancy?\n\n[41:35] Where to next?\n\n[51:29] Vivian's supplemental comment on neutri no mass constraints\n\n[52:38] Keir - follow-up coming from DESI\n\n[52:59] What current work in cosmology is particular ly underappreciated by the community?\n\n[55:23] Final question to Keir about how these findings relate to work discussed in an earlier Cosmology Talk\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/76/ END:VEVENT BEGIN:VEVENT SUMMARY:Lamman\, Legnani\, Shi\, Sarcevic\, Pyne\, and Ferreira DTSTART:20240221T050000Z DTEND:20240221T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/77 DESCRIPTION:Title: Intrinsic Alignments: A Guide for Everyone\nby Lamman\, Legnani\, Shi\, Sarcevic\, Pyne\, and Ferreira as part of Cosmology Talks \n\n\nAbstract\nClaire Lamman\, Jingjing Shi\, Niko Šarčević\, Susan Py ne\, Elisa Legnani and Tassia Ferreira tell us about the intrinsic alignme nts guide they wrote (along with Eleni Tsaprazi\, who couldn’t make the video recording).\n\nThey wanted to write something that wasn’t quite a review\, but also wasn’t quite a set of lecture notes. Instead they aime d for what might be best framed as a “cheat sheet” for intrinsic align ments. Everything you need to know about the topic\, compressed into one a rticle. However\, there’s still a lot about the topic\, so the compressi on is still 33 pages and 10 figures big.\n\nTo construct the guide they br oke the topic of intrinsic alignments into sub-fields and then asked quest ions like “what are the key equations for this sub-field?”\, “what a re the different notations people use?”\, “what might be confusing to a newcomer?” They then wrote the guide to answer those questions\, even including subsections with quick definitions of each common term\, and sho rt lists of common alternative notations.\n\nIn this video they go over bo th the guide and the topic of intrinsic alignments.\n\nVideo: youtu.be/BlibRW4XpR8\n\nPaper: arXiv:2309.08605 \n\n\nClaire: cmlamman.github.io/\n\nJingjing: jshiastro.com\n\nNiko: nikosarcevic.com\n\nSusan: www.ucl.ac.uk /astrophysics/susan-pyne-honorary-research-fellow\n\nElisa: elisalegnani.github.io\n\nTassia: physics.ox.ac.uk/o ur-people/ferreirat\n\nEleni: https://t saprazi.eu\n\n\n
\n\nIndex to Key Parts of the Talk\n\n[0:00 :00] Shaun's intro\n\n[0:0 1:13] What are intrinsic alig nments? plus IA cheat sheet\n\n[0:02:54] Two things to remember from this talk\n\n[0:03:17] Getting into the background an d details\n\n[0:10:04] E llipticity (section 2 of paper*)\n\n[0:12:38] Galaxy types and shapes\n\n[0:16:31] IA Correlation Function Notation (secti on 4*)\n\n[0:19:02] IA Correlation Functions (section 5*)\n\n[0:23:01] Correlations\n\n[0:23:34] Shear (section 3*)\n\n[0:30:54] 3D IA Power Spectrum (section 6*) \n\n[0:38:33] 2D IA Power Sp ectrum (section 7*)\n\n[0:46:01] Modeling (section 8*)\n\n[1:00:41] Where to next?\n\n[1:06:44] What current work in cosmology is particularly underappreciated by the community?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/77/ END:VEVENT BEGIN:VEVENT SUMMARY:Pritha Paul\, Chris Clarkson (QMUL) DTSTART:20240308T050000Z DTEND:20240308T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/78 DESCRIPTION:Title: There is Parity Violation in Standard Observational Cosmolo gy\nby Pritha Paul\, Chris Clarkson (QMUL) as part of Cosmology Talks\ n\n\nAbstract\nThere is Parity Violation in Standard Observational Cosmolo gy (Pritha Paul and Chris Clarkson)\n\nPritha Paul and Chris Clarkson tell us about their work\, along with Roy Maartens\, delving very deeply into standard observational cosmology. Specifically\, they have looked at relat ivistic effects in the four point function/trispectrum of galaxy positions .\n\nThis might sound crazy and masochistic\, but there are big rewards. O n large enough scales\, the relativistic effects start to grow\, and tanta lisingly\, once one takes into account both relativistic effects and the o bservational effects of observing in redshift space\, a parity violating s ignal emerges in both the bispectrum and trispectrum on large scales. This is very interesting given the possible observations of parity violation i n the four point function of galaxy positions (i.e. Fourier transform of t he trispectrum).\n\nThere are reasons to suspect the effect Pritha\, Chris and Roy have uncovered within standard cosmology couldn't be the thing po tentially observed in the four point function\, however it is possible to at least tell a story about how the one effect might show up in the other observation. Time will tell whether they are indeed related.\n\nIrrespecti ve of that\, the result is still interesting as it is likely that Euclid a nd/or SKA will be able to spot this signal\, thus detecting the effects of relativity within the large scale structure.\n\nTalk recording on the Cosmology Talks youtube channel\n\ nPritha's QMUL profile page\n\nChris' QMUL profile pag e\n\nPaper: arXiv: 2402.164 78\n\n
\n\nIndex to Key Parts of the Talk\n\n[00:00] Shaun's intro\n\n[01:26] Overview by Pritha and Chris and 2 ta keaways from the talk\n\n[02:34] What is the motivation for this work?\n\n[05:03] Why the 4-pt correlation function is nee ded\n\n[05:58] Recent wo rk by others\n\n[09:37] Large Scale Surveys\n\n[11:35] Real Space to Redshift Space - Power Spectrum\n\n[15:36] Real Space to Redshift Space - Bip ectrum\n\n[19:38] Tree Level Trispectrum\n\n[20:59] Trispectrum Geometry\n\n[21:43] Third order number counts\n\n[26:30] Trispectrum\n\n[26:55] Calculating the Trispectrum\n\n[30:50] 15-min Q & A segment\n\n[ 46:10] What current work in cosmology is particularly underappreciated by the community?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/78/ END:VEVENT BEGIN:VEVENT SUMMARY:Sylvia Wenmachers (Institute of Philosophy\, KU Leuven) DTSTART:20240316T050000Z DTEND:20240316T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/79 DESCRIPTION:Title: New Probability Axioms Could Fix Cosmology's Multiverse (Pa rtially)\nby Sylvia Wenmachers (Institute of Philosophy\, KU Leuven) a s part of Cosmology Talks\n\n\nAbstract\nSylvia is a philosopher of scienc e. Her focus is probability and she has worked on a few theories that aim to extend and modify the standard axioms of probability in order to tackle paradoxes related to infinite spaces. In particular there is a paradox of the "infinite fair lottery" where within standard probability it seems im possible to write down a "fair" probability function on the integers. If y ou give the integers any non-zero probability\, the total probability of a ll integers is unbounded\, so the function is not normalisable. If you giv e the integers zero probability\, the total probability of all integers is also zero. No other option seems viable for a fair distribution.\n\nThis paradox arises in a number of places within cosmology\, especially in the context of eternal inflation and a possible multiverse of big bangs bubbli ng off. If every bubble is to be treated fairly\, and there will ultimatel y be an unbounded number of them\, how do we assign probability?\n\nThe pr oposed solutions involve hyper-real numbers\, such as infinitesimals and i nfinities with different relative sizes\, (reflecting how quickly things c onverge or diverge respectively).\n\nThe multiverse has other problems\, a nd other areas of cosmology where this issue arises also have their own pr oblems (e.g. the initial conditions of inflation)\; however this could ver y well be part of the way towards fixing the cosmological multiverse.\n\nT alk recording: youtu.be/MBeSoig4DPY \n\nSylvia: sylviawenmacker s.be\n\nPaper: arXiv: 2308. 12229\n\n
\n\n[0:00:00] Shaun's intro\n\n[0:02:17] Sylvia's overview\n\n[0:03:49] Two takeaways from this talk\n\n[0:06:36] The motivation and reason for timing of this work\n\n[0:09:54] Two pr obabilistic questions\n\n[0:10:22] 1. Probability of inflation\n\n[0:11:03] 2. Predictability problem\n\n[0:14:27] Infinite phase space\n\n[0: 16:01] Probability formalism s\n\n[0:19:20] Paradox: fair infinite lottery\n\n[0:20:56] Standard probability theory\n\n[0:23:07] Paradox: fair lottery on N\n\n[0:26:40] Finitely additive probabil ity\n\n[0:33:00] Non-Ar chimedean probability\n\n[0:41:10] Non-normal quasi-probability\n\n[0:45:27] Infinite lottery logic (ILL)\n\n[0:47:5 3] Implications for inflati on theory?\n\n[1:02:05] Where to next?\n\n[1:08:27] What current work in cosmology is particularly underappreciated by t he community?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/79/ END:VEVENT BEGIN:VEVENT SUMMARY:Andreu Font-Ribera\, Seshadri Nadathur (IFAE\, U of Portsmouth) DTSTART:20240404T050000Z DTEND:20240404T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/80 DESCRIPTION:Title: DESI 2024 - Cosmological Constraints from BAO (Font-Ribera and Nadathur)\nby Andreu Font-Ribera\, Seshadri Nadathur (IFAE\, U of Portsmouth) as part of Cosmology Talks\n\n\nAbstract\nThe Dark Energy Spec troscopic Instrument (DESI) has produced cosmological constraints! And it is living up to its name.\n\nTwo researchers from DESI\, Seshadri Nadathur and Andreu Font-Ribera\, tell us about DESI's measurements of the Baryon Acoustic Oscillations (BAO) released today. These results use one full yea r of DESI data and are the first cosmological constraints from the telesco pe that have been released.\n\nMostly\, it is what you might expect: tight er constraints. However\, in the realm of the equation of state of dark en ergy\, they find\, even with BAO alone\, that there is a hint of evidence for evolving dark energy. When they combine their data with CMB and Supern ovae\, who both also find small hints of evolving dark energy on their own \, the evidence for dark energy not being a cosmological constant jumps as high as 3.9σ with one combination of the datasets.\n\nIt seems there sti ll is "concordance cosmology"\, it's just not ΛCDM for these datasets.\n\ nThe fact that all three probes are tentatively favouring this is intrigui ng\, as it makes it unlikely to be due to systematic errors in one measure ment pipeline.\n\nWatch this space for updates!\n\nVideo recording: youtu.be/9DsMphPfrjI\n\nThe papers: < a href="https://data.desi.lbl.gov/doc/papers/">data.desi.lbl.gov/doc/paper s/\n\narXiv: 2404.03000\, 2404.03001\, 2404.03002\n\nDESI: desi.lbl.gov/\n\nAndreu: andreufont.github.io/\n\nSesh: seshnadathur.github.io/\n\n
\n\nIndex to Key Pa rts of the Talk\n\n[0:00:00] Shaun's intro\n\n[0:00:36] Opening overview and quick peak of results by Andreu and Sesh\n\n [0:01:37] BAO results from DE SI DR1\n\n[0:02:14] DESI BAO and Dark Energy\n\n[0:04:54] DESI BAO and neutrino masses\n\n[0:05:18] DESI BAO and the Hubble Tension\n\n[0:06:3 1] Main talk: background\, d etails\, results (starting with BAO)\n\n[0:09:43] DESI: the instrument\n\n[0:11:05] DESI: the survey\n\n[0:12:04] DESI Data Release 1 (DR1)\n\ n[0:18:11] BAO measurements with galaxies & quasars at z<2\n\n[0:21:32] Non-linear evolution and Density field reconstructio n\n\n[0:23:41] How is t he DESI BAO analysis different?\n\n[0:30:08] Tests of systematic errors\n\n[0:34:02] Unblinded data results!\n\n[0:3 9:16] BAO measurements from the Lyman-α forest at z>2\n\n[0:45:16] Lyα BAO: Analysis Validation\n\n[0:48:41] Lyα BAO: Unblinding!\n\n[0:51:1 0] DESI DR1 Lyα BAO: Publi cations\n\n[0:53:42] Co smological Constraints: Flat ΛCDM from DESI BAO\n\n[0:58:02] Breaking the H_0-r_d degeneracy \n\n[1:01:35] DESI BAO and the Hubble Tension\n\n[1:03:54] DESI BAO and neutrino masses\n\n[1:10:52] DESI BAO and Dark Energy\n\n[1:23:06] Summary\n\n[1:24:00] What's next?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/80/ END:VEVENT BEGIN:VEVENT SUMMARY:Russell Boey\, Richard Easther\, Yourong Frank Wang (University of Auckland) DTSTART:20240411T060000Z DTEND:20240411T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/81 DESCRIPTION:Title: Black Holes in Ultralight Dark Matter - Slowed Down and Spe d Up?\nby Russell Boey\, Richard Easther\, Yourong Frank Wang (Univers ity of Auckland) as part of Cosmology Talks\n\n\nAbstract\nRussell Boey\, along with his coauthors Richard Easther and Yourong Wang\, tells us about his simulations of a supermassive blackhole travelling through an ultrali ght dark matter soliton. In particular\, he has studied the dynamical fric tion effect on the blackhole within the soliton. \n\nThis is especially in teresting in the context of the "final parsec" problem\, where the orbits of supermassive blackhole binary systems stall in their decay as they reac h one parsec separation. Maybe a different background\, in the form of ULD M instead of WIMP DM\, could help?\n\nAn ultralight dark matter soliton is much more dense than expectations from "ordinary" WIMP-like dark matter\, so it is also expected that the dynamical friction in such a soliton shou ld be large. This is indeed what Russell\, Richard and Yourong found (and other coauthor Emily Kendall who isn't present in the video). However\, cu riously\, they also found a secondary effect where the blackhole perturbs the soliton\, which in turn causes the soliton to backreact on the blackho le and sometimes speed it back up.\n\nThere is definitely interesting phys ics to explore inside galaxies in ultralight dark matter systems\, but no verdict just yet on whether the final parsec has been overcome or not.\n\n Talk recording: https://www.youtube.com/watch?v=hyf6VtbZ6-c\n\nRussell: ht tps://profiles.auckland.ac.nz/russell-boey\n\nRichard: https://profiles.au ckland.ac.nz/r-easther/about\n\nYourong: https://fwphys.com/\n\nThe paper: https://arxiv.org/abs/2403.09038\n\nThe earlier paper: https://arxiv.org/ abs/2110.03428\n\n
\n\nIndex to Key Parts of the Talk\n\n[00:00] Shaun's intro\n\n[01:14] Opening remarks by Russell\n\n[02:02] Two things to r emember about this talk\n\n[04:08] Motivation for this work (The Final Parsec Problem)\n\n[06: 49] Ultralight Dark Matter\n\n[09:07] Objective\ n\n[12:10] Explaining use of the Schrodinger-Poisson equations\n\n[13:44] Getting into the details - Setup\n\n[17:14] Dynamical Friction Theory\n \n[22:24] Semi-Analytic Mod el\n\n[25:28] Simulatio n Behavior\n\n[30:01] N umerical Dependencies\n\n[33:19] Black Hole Mass Dependence\n\n[34:46] ULDM Mass Dependence\n\n[36:38] Soliton Mass Dependence\n\n[38:22] < a href="https://youtu.be/hyf6VtbZ6-c?t=2302s">Semi Analytic Model Comparis on\n\n[40:51] Overdensi ties\n\n[43:12] Force C omparison\n\n[45:40] Co nclusion\n\n[51:48] Wha t next?\n\n[56:34] What current work in cosmology is interesting but underappreciated by the comm unity?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/81/ END:VEVENT BEGIN:VEVENT SUMMARY:Minh Nguyen\, Beatriz Tucci (University of Michigan\, Max-Planck-I nstitut für Astrophysik) DTSTART:20240503T060000Z DTEND:20240503T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/82 DESCRIPTION:Title: Field Level Inference - Up to 5 sigma Better than Power and Bispectrum!\nby Minh Nguyen\, Beatriz Tucci (University of Michigan\, Max-Planck-Institut für Astrophysik) as part of Cosmology Talks\n\n\nAbs tract\nNhat-Minh Nguyen and Beatrice Tucci tell us about their recent work comparing the performance of field inference (FLI) and simulation based i nference (SBI). In an apples to apples comparison\, they find that FLI com fortably outperforms SBI\, even in what is essentially the "best case scen ario" for SBI.\n\nField level inference gives up on using "summary statist ics" to construct a cosmological likelihood (e.g. the power spectrum\, the bispectrum\, the location of the BAO peak\, voids\, etc) and instead cons tructs the cosmological likelihood at the level of the field itself. In ot her words the likelihood step of a statistical analysis is done comparing the measured density field at each point in Fourier space to a model's act ual density field. This means the set of model "parameters" necessarily al so includes the entire set of Fourier modes of the initial conditions. The n\, for example\, when one would then talk about the "maximum likelihood" parameters in a FLI inference\, one is talking also about the maximum like lihood set of initial conditions.\n\nOne then does the rest of the statist ical analysis more or less the same as if one is analysing a measured powe r spectrum\, e.g. one has priors on the inferred parameters\, one has the likelihood function\, and one produces posterior probability distributions for all of the model parameters.\n\nIn this analysis they fixed all cosmo logical parameters except the overall amplitude of the initial density flu ctuations\, via σ8. This means they also restricted the set of initial de nsity fluctuations to those with a certain spectral index\, but varied ove r all sets of initial density fluctuations that do produce this spectral i ndex. They then evolve the initial conditions forward in time using the LE FTfield framework and do the FLI analysis on the evolved field. \n\nSBI however still uses summary statistics\, in this case the power spe ctrum and bispectrum\, but uses simulations to construct the likelihood\, rather than making model based assumptions for what these statistics shoul d look like.\n\nIn this analysis they are only comparing the performance o f FLI and SBI at reconstructing the parameters of simulations\, because th e observed data in e.g. BOSS or DESI is only well-calibrated at the level of the power spectrum (and maybe the bispectrum?)\, but not the full non-l inear density field that FLI can probe - and where its true improvements l ie.\n\nHowever\, they find FLI outperforms SBI with error bars substantial ly smaller (by factors of 2-5 depending on the scales and simulations cons idered). This shows that if we could perform field level inference on curr ent or future data sets\, the level of constraints we could obtain would a lso be substantially improved (e.g\, maybe even a 1σ deviation would beco me a 5σ detection!?)\n\nRecorded Talk Video: youtu.be/Pxfsf89jZwI\n\nMinh: minhmpa.github.io/\n\nBeatriz: wwwmpa.mpa-garching.mpg.de/~tucci/\n\nPaper: arXiv:2403.03220\n\n
\n\nIndex to Key Parts of the Talk\n\n[00:00] Shaun's intro\n\n[01:20] Opening remarks by Minh and Beatriz\n\ n[02:39] Takeaways to rememb er about this talk\n\n[05:48] Motivation for this work\n\n[08:45] Getting into the details: Amplitude of Structure Growth< /a>\n\n[09:52] Galaxy cluste ring can distinguish scenarios of new physics\n\n[10:49] Galaxy bias - response of galaxy formatio n to fluctuations\n\n[11:47] Galaxy bias spoils constraint from galaxy clustering\n\n[12:30] < a href="https://youtu.be/Pxfsf89jZwI?t=750s">Effective Field Theory of gal axy bias\n\n[15:45] FBI (field-level Bayesian inference) and SBI (simulation-based inference) post eriors\n\n[18:46] Exten ded discussion at the Field-Level Inference slide\n\n[29:17] Apple-to-apple comparison of FBI and SBI P+B\n\n[31:12] Sim ulation-based inference\n\n[33:06] Neural Posterior Estimation (NPE)\n\n[34:35] Normalizing flows\n\n[35:37] SBI wrap-up putting it all togethe r\n\n[40:37] Improvemen t increases with scale cuts\n\n[43:02] Robust improvement across samples\n\n[44:50] Where to next?\n\n[49:30] What current work in cosmology is interesting but underappreciated by the community?\n\n[50:24] Beyond 2-point mock data challenge \n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/82/ END:VEVENT BEGIN:VEVENT SUMMARY:Mark Fromhold\, Lucia Hackermuller (University of Nottingham) DTSTART:20240523T060000Z DTEND:20240523T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/83 DESCRIPTION:Title: Fundamental Cosmology from the Lab\nby Mark Fromhold\, Lucia Hackermuller (University of Nottingham) as part of Cosmology Talks\n \n\nAbstract\nMark Fromhold and Lucia Hackermuller tell us about how they are 3D printing atom traps that allow them to cool atoms to a few micro Ke lvin. This is super interesting for cosmology because it would allow them\ , among many other things\, to potentially trap dark domain walls. We lear ned in another recent cosmology talk about the physics behind these dark d omain walls\, now here is the physics behind the cold atom trap.\n\nIn pri nciple these traps may one day measure the gravitational effects of quantu m objects\, ultimately testing whether space-time curvature can be in a qu antum superposition or not.\n\nTalk video: https://youtu.be/1XAbMkoQeXg\n\ nLucia: https://www.nottingham.ac.uk/physics/people/lucia.hackermuller\n\n Mark: https://www.nottingham.ac.uk/physics/people/mark.fromhold\n\nDark Do main Walls: https://arxiv.org/abs/2308.01179\n\n
\nIndex to Key Part s of the Talk\n\n[00:00] S haun's intro\n\n[01:04] O pening remarks by Lucia and Mark\n\n[04:47] Timing & enabling investments in Quantum 2.0 technolog ies\n\n[09:18] How are a toms cooled to <1 millionth degree above absolute zero?\n\n[15:50] Ultracold atoms\, setup in the lab\, laser system\n\n[20:12] Movie - Lithium MOT\n\n[21:05] Evaporative cooling - Lithium\n\n[26:02] Li_2 Bose-Einstein Condensate\n\n[27: 47] Quantum 2.0 sensors \n\n[32:15] 3D printed cham bers\n\n[34:23] Printed surfaces\n\n[35:17] Pa rts for Quantum 2.0 technologies\; New manufacturing techniques\n\n[37 :53] New hybrid shielding/m agnetic bias product\n\n[39:34] Printed vapour cells\n\n[41:34] Spectroscopy and magnetic sensors\n\n[42:36] Compact\, printed Laser system \n\n[44:22] A printed gravi meter for space\n\n[46:16] Printed cold atom system\n\n[49:35] Where to next?\n\n[53:42] Other ideas on the horizon?\n\n[58:02] What current work in cold atoms is int eresting but underappreciated?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/83/ END:VEVENT BEGIN:VEVENT SUMMARY:Elisabeth Krause++ (University of Arizona) DTSTART:20240606T060000Z DTEND:20240606T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/84 DESCRIPTION:Title: The Parameter Masked Mock Data Challenge for Beyond 2-Pt St atistics - Results\, Lessons & Reflections\nby Elisabeth Krause++ (Uni versity of Arizona) as part of Cosmology Talks\n\n\nAbstract\n1-1/2 hour d iscussion with Shaun Hotchkiss and 9 members of The Beyond-2pt Collaborati on: Elisabeth Krause\, Marcos Pellejero-Ibanez\, Andres Salcedo\, Minh Ngu yen\, Mikhail Ivanov\, Enrique Paillas\, Carolina Cuesta-Lazaro\, Chirag M odi\, Giovanni Verza\n\nOne-sentence summary of the work by Minh Nguyen: " how cosmology and galaxy survey analyses can move beyond the canonical 2-p oint correlation function"\n\nRecorded video: youtu.be/LPykO2206OY\n\nPaper: arXiv:2405.02252\n\n
\n\nIndex to Key Parts of th e Talk\n\n[0:00:00] Shaun' s intro\n\n[0:02:05] Ope ning comments by Elisabeth Krause\n\n[0:03:13] Two things to remember about this talk\n\n[0:04 :56] The history of this ide a\n\n[0:06:19] Why the t eam used this approach\n\n[0:08:43] Getting into the details\n\n[0:13:31] Redshift-space results in σ8 and Ωm (Figs. 21\ , 1 in paper)\n\n[0:18:10] Light-cone and Real-space Results (Figs 3\, 4)\n\n[0:19:28] Takeaways\n\n[0:22:53] The Methods and How They Work: Pa rticipating Analyses (Table 1)\n\n[0:24:14] Importance of k_max\n\n[0:27:18] Overview of EFT Methods\n\n[0:35:47] Overview of HOD Methods\n \n[0:41:43] 2-min overviews of each specific method\n\n[0:55:50] Post unmasking insights and updated results\n\n[1:04:49 ] Lessons learned and futur e reflections\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/84/ END:VEVENT BEGIN:VEVENT SUMMARY:Tamara Davis\, Maria Vincenzi\, Dillon Brout (DES Collaboration) DTSTART:20240610T060000Z DTEND:20240610T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/85 DESCRIPTION:Title: The Dark Energy Survey Supernova Program - Data and Cosmolo gy\nby Tamara Davis\, Maria Vincenzi\, Dillon Brout (DES Collaboration ) as part of Cosmology Talks\n\n\nAbstract\nTamara Davis\, Maria Vincenzi and Dillon Brout tell us about the Dark Energy Survey's (DES) new supernov a catalogue. The catalogue has more than 1500 new supernovae\, and will al low a vast range of new cosmology constraints. It is a factor of around fi ve larger than the next largest high redshift supernovae catalogue.\n\nVer y curiously\, DES' supernovae see hints of evolving dark energy. This is e specially curious given that a few months after DES released this data\, t he Dark Energy Spectroscopic Instrument (DESI) also released data with sim ilar hints.\n\nTamara: smp.uq.edu.au - tamara-davis\n\nMaria: linkedin - maria-vincenzi\n\nDi llon: djbrout.github.io\n\nKey co smology paper: arXiv: 2401.0292 9\n\nCosmological Analysis and Systematic Uncertainties: arXiv: 2401.02945\n\nLight curves and 5- Year data release: arXiv: 2406. 05046\n\n
\n\nIndex to Key Parts of the Talk\n\n[0:00:00] Shaun's intro\n\n[0:01:11] < a href="https://youtu.be/y9ocwGJnGwk?t=71">Intro by the 3 speakers to this work\n\n[0:02:43] Two ta keaways to remember\n\n[0:05:54] Supernova cosmology basics\n\n[0:29:47] DES Analysis Details\n\n[0:48: 10] DES SN Cosmology Results \n\n[1:00:09] Is dark en ergy a cosmological constant? \n\n[1:01:22] A few months later...DESI supports DES\, finding simil ar result for wa\n\n[1:02:39] Big Questions: Is the expansion of the Universe accelerat ing? Yes! \n\n[1:03:35] Big Questions: Is dark energy a cosmological constant? Maybe? Union 3 also prefer w > -1\n\n[1:10:23] Big Questions: How old is the Universe? Slightly younger than we thou ght?\n\n[1:11:12] Big Qu estions: Does DES best fit resolve Hubble tension? No\, DES doesn't constr ain H0\n\n[1:12:04] Bonus Science!!!\n\n[1:16:08] Cosmology work interesting but underappreciated?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/85/ END:VEVENT BEGIN:VEVENT SUMMARY:Ryan Camilleri\, Tamara Davis (DES Collaboration\, University of Q ueensland) DTSTART:20240611T060000Z DTEND:20240611T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/86 DESCRIPTION:Title: DES Supernovae - H0 From the Inverse Distance Ladder Withou t ΛCDM\nby Ryan Camilleri\, Tamara Davis (DES Collaboration\, Univers ity of Queensland) as part of Cosmology Talks\n\n\nAbstract\nRyan Camiller i and Tamara Davis tell us about how they have used the Dark Energy Survey 's Year 5 supernovae catalogue\, anchored to the Dark Energy Spectroscopic Instrument's Baryon Acoustic Oscillations\, to create an "inverse distanc e ladder".\n\nWith this they are able to determine the Hubble Parameter\, at redshift zero with a high accuracy\, without needing to assume ΛCDM. T he results still match Planck\, meaning that the high redshift to low reds hift matching appears to still not work out\, even outside of ΛCDM.\n\nTh e implications are large for any attempts to go beyond ΛCDM to solve the Hubble tension as it appears the z=2 to z=0.05 window is not the right win dow for finding the solution.\n\nVideo recording: youtu.be/kzT0tWWggRo\n\nPaper: arXiv: 2406.05049\n\nRyan: smp.uq.edu.au/profile/13102/ryan-cami lleri\n\nTamara: smp.uq.edu.au/profile/186/tamara-davis\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/86/ END:VEVENT BEGIN:VEVENT SUMMARY:Ryan Camilleri\, Tamara Davis (DES Collaboration\, University of Q ueensland) DTSTART:20240612T060000Z DTEND:20240612T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/87 DESCRIPTION:Title: DES Supernovae - Beyond ΛCDM\nby Ryan Camilleri\, Tama ra Davis (DES Collaboration\, University of Queensland) as part of Cosmolo gy Talks\n\n\nAbstract\nRyan Camilleri and Tamara Davis tell us about how they have examined models beyond ΛCDM using the Dark Energy Survey's wond erful supernova catalogue. Tantalisingly\, they find that a number of mode ls are "moderately preferred" over ΛCDM (in model comparison speak).\n\nT hey also\, very admirably\, check whether crucial aspects of the DES pipel ine are model dependent or not. They find that\, so long as the reference model is close-ish to the true model then the pipeline is accurate. "Close -ish" is very generous here as well\, as they even found in simulations th at when one processed the data with models 10σ from the truth\, the subse quent parameter constraints were still within 1σ of the truth. The moral of this is that\, even though the supernovae were processed assuming ΛCDM \, so long as the true cosmology isn't too far from ΛCDM then this doesn' t matter.\n\nThis means\, if you have your own model that they haven't tes ted\, you don't need to simulate the entire DES analysis pipeline to analy sis your model\, you can do your model comparison at the level of the Hubb le diagram. Nice!\n\nTalk video: yo utu.be/NLXxX-Z2OfM\n\nPaper: arXiv: 2406.05048\n\nRyan: smp.uq.edu.au/profile/13102/ryan-camilleri\n\nTama ra: smp.uq.edu.au /profile/186/tamara-davis\n\n
\n\nIndex to Key Parts of the Talk \n\n[00:00] Shaun's intro< /a>\n\n[01:41] Opening comme nts by Ryan\n\n[02:20] T wo takeaways to remember\n\n[03:06] Motivation for this work\, starting with ΛCDM overview\n\ n[05:01] So why go beyond Λ CDM?\n\n[06:13] What is beyond ΛCDM? Testing different models\n\n[07:18] Parametric forms of Λ\n\n[09:28] Dvali-Gabadadze-Porrati (DBP) models\n\n[10:04] Chaplygin Gas models\n\n[11:13] Timesc ape cosmology\n\n[14:12] Why these models were tested vs other options?\n\n[15:31] Observations -> Hubble Diagram\n\n[ 16:08] DES-SN5YR Pipeline\n\n[23:10] The Omega\\_m - w degeneracy\; intro of Q_H parameter\n\n[25:21] Model constraints\n\n[29:43] Model comparisons\n\n[35:37] What's next?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/87/ END:VEVENT BEGIN:VEVENT SUMMARY:Paul Shah\, Tamara Davis (DES Collaboration\, University College L ondon\, University of Queensland) DTSTART:20240617T060000Z DTEND:20240617T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/88 DESCRIPTION:Title: DES Supernovae - Weak Lensing Magnification Detected at 6σ !\nby Paul Shah\, Tamara Davis (DES Collaboration\, University College London\, University of Queensland) as part of Cosmology Talks\n\n\nAbstra ct\nPaul Shah and Tamara Davis tell us about how they have used this wonde rful supernova catalogue from the Dark Energy Survey to detect the weak le nsing magnification signal for the first time. There has been evidence of this signal in earlier catalogues\, but at no bigger than 1.4σ. They've g ot it at 6σ!\n\nThey do this by correlating the scatter in the magnitude of the supernovae with the over-under density in galaxy catalogues along t he same lines of sight of the supernovae. Where there is more matter\, the light from the supernova should be magnified\, and where there is less ma tter it should be de-maginified. And they do indeed see that along overden se lines of sight the supernovae are\, on average\, ever so slightly brigh ter\, and on underdense lines of sight the are ever so slightly dimmer.\n\ nI can't wait to see how this observable is used in the future to constrai n all sorts of bits of cosmology. Nice work everyone!\n\nTalk Video: youtu.be/YljnmVZKukc\n\nPaper: arXiv: 2406.05047\n\nPaul: paulshah.github.io\n\nTamara: smp.uq.edu.au/profile/18 6/tamara-davis\n\n
\n\nIndex to Key Parts of the Talk\n\n[00 :00] Shaun's intro\n\n[01: 20] Searching for gravitation al lensing of SNe\n\n[04:24] Two takeaways to remember\n\n[05:43] Motivation for this work and why it could be done now\n\n[10:22] The Hubble diag ram of SN Ia\n\n[11:16] What does a clumpy universe do to SN Ia?\n\n[13:37] But can we detect it?\n\n[14:46] Our data\n\n[16:37] Our lensing estimator\n\n[20:52] Correlate lensing estimate with Hubble diagram residuals\n\n[27:01] The shape of dark matter haloes\n\n[27:43] 'Adaptive optics' for dark matter\n\ n[30:49] What's next?\n \n[34:23] Key results from DES-SN5YR weak lensing\n\n[45:05] Further work anticipated?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/88/ END:VEVENT BEGIN:VEVENT SUMMARY:Ryan White\, Tamara Davis (DES Collaboration\, University of Queen sland) DTSTART:20240619T060000Z DTEND:20240619T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/89 DESCRIPTION:Title: DES Supernovae - Precisely Measured Time Dilation from Univ erse's Expansion\nby Ryan White\, Tamara Davis (DES Collaboration\, Un iversity of Queensland) as part of Cosmology Talks\n\n\nAbstract\nRyan Whi te and Tamara Davis from the Dark Energy Survey tell us about how they hav e measured time dilation in distant supernovae. This time dilation is prec isely what one would expect in an expanding universe. "Precisely" is the r ight word too\, as they have measured this effect to 0.5% precision and th ey get exactly the number predicted by an expanding universe.\n\nThere may be all sorts of tensions popping up for the standard cosmological model ΛCDM\, but it seems the expanding universe itself is doing just fine.\n\n Talk video: youtu.be/1vfo-JFc-Io\n\nRyan: ryanwhite1.github.io\n\nTamara: smp. uq.edu.au/profile/186/tamara-davis\n\nThe paper: arXiv: 2406.05050\n\nThe paper with the \\Delta t = (1+z) proof (in appendix A): arXiv: 0804.3595\n\n
\n\nIndex to Key Parts of the Talk\n\n [00:00] Shaun's intro\n\n[ 02:46] Overview of this work by Ryan and Tamara\n\n[06:08] Supernova light curves in different bands across redshifts\n\n[ 10:55] Picking similar light curves out of different bands\n\n[11:23] Stacked light curves\n\n[13:55] Scale light curves in time by function of source z\n\n[18:02] The 'widt h' of each individual light curve\n\n[18:43] Quantifying time dilation\n\n[21:44] Why do we expect time dilation?\n\ n[27:58] Scatter in widths from noise & intrinsic SN light curve variation\n\n[38:00] Where to next?\n\n[40:56] What current cosmology work is inte resting but underappreciated?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/89/ END:VEVENT BEGIN:VEVENT SUMMARY:Wendy Freedman\, Barry Madore (Chicago Carnegie Hubble Program (CC HP)) DTSTART:20240816T060000Z DTEND:20240816T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/90 DESCRIPTION:Title: The Status of the Chicago-Carnegie Hubble Program (with JWS T data)\nby Wendy Freedman\, Barry Madore (Chicago Carnegie Hubble Pro gram (CCHP)) as part of Cosmology Talks\n\n\nAbstract\nWendy Freedman and Barry Madore give a status update on the Chicago-Carnegie Hubble Program ( CCHP). There has been much progress!\n\nIn this status update there are th ree independent distance ladder measurements of the expansion rate (i.e. t he Hubble parameter) all using JWST data. There is the very well-known Cep heid method\, the now also well known Tip of the Red Giant (TRGB) method\, and making its debut\, the J-Region Asymptotic Giant Branch (JAGB) method . \n\nThe TRGB and JAGB methods agree strikingly well and appear to be con sistent with the CMB + ΛCDM value for the expansion rate. The Cepheid met hod also agrees to within less than 5%\, which is still striking\, but the re is some deviation.\n\nThe deviation pushes the Cepheid value for H0 up\ , making it consistent with the SH0ES value\, although the error bars on t his CCHP result are large enough that their Cepheid value is also consiste nt with the lower TRGB and JAGB methods. Most curiously (to this relative outsider) the JAGB value does not appear to be consistent with SH0ES\, eve n when considering statistical and systematic errors at once. The striking consistency between TRGB and JAGB\, means that one's naive guess might be that there is some unknown systematic in the Cepheid method (in both the CCHP and SH0ES measurements). However\, naive guesses are naive so\, time will tell.\n\nTime really will tell as the ongoing JWST measure ments will shrink both statistical and systematic errors in all methods\, so it won't be long before the CCHP Cepheids are forced to take a side.\n\ nVideo recording: youtu.be/OkGUoKuk wk8\n\nWendy: astro.uchicago.edu/people/wendy-l-freedman.php\n\nBarry: carnegiesci ence.edu/bio/dr-barry-madore-emeritus\n\nPaper: arXiv: 2408.06153\n\n
\n\n[0:00:00] Intro comments by Shaun and Wendy\n\ n[0:01:22] Two takeaways to r emember\n\n[0:01:47] Not seeing now *extraordinary evidence* for Hubble tension\; unknown systemat ics\n\n[0:03:18] Backgro und on gold standard methods for measuring H0\n\n[0:09:05] 2 methods agree in their zero point\, l ow scatter against each other\n\n[0:09:35] 2 new papers on arXiv and recent CCHP group papers\; mo re coming\n\n[0:11:58] F irst target galaxies\; TRGB and JAGB advantages\; HST cf JWST\n\n[0:20 :54] 3 distances indicators - TRGB\, Cepheids\, JAGB\n\n[0:29:14] JAGB details\n\n[0:31:29] Data Analysis\n\n[0:32:31] Comparison of distances (pre a determination of H0) \n\n[0:36:09] TRGB vs J AGB comparison\n\n[0:38:22] SN Calibrator M_B with Distance Modulus (potential systematic needs u nderstanding)\n\n[0:42:02] Carnegie Supernova Project\n\n[0:44:12] Summary of H0 Values and Statistical Uncertainties (T able 4 in paper)\n\n[0:51:09] Distribution of H0 Values for 3 JWST Methods( Fig. 11)\n\n[0:52 :45] Distribution of H0 Val ues With Total Errors (Fig. 12)\n\n[0:53:21] CCHP JWST H0 Values (Fig. 20)\n\n[0:58:38] Conclusions (TRGB\, JAGB agree a t 1% level\; results consistent with Planck\, LCDM\n\n[1:02:27] What might be cause of high H0 wi th Cepheids?\n\n[1:06:28] What about the possibility of new physics?\n\n[1:09:06] What current work in cosmology is inte resting but underappreciated?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/90/ END:VEVENT BEGIN:VEVENT SUMMARY:Abigail J. Lee (University of Chicago) DTSTART:20240822T060000Z DTEND:20240822T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/91 DESCRIPTION:Title: Extragalactic Distances from the J-region Asymptotic Giant Branch\nby Abigail J. Lee (University of Chicago) as part of Cosmology Talks\n\n\nAbstract\nAbigail Lee tells us about how she has used the J-re gion Asymptotic Giant Branch (JAGB) to measure extragalactic distances\, u ltimately using them as a rung on the distance ladder to measure the expan sion rate of the universe.\n\nThe JAGB method is new\, at least compared t o cepheids and "tip of the red giant" (TRGB) methods\, but is also very pr omising. The stars it uses are bright\, so they can be seen at large dista nces\, and they're numerous\, which means they can be observed far from th e centres of galaxies (minimising "crowding" from other stars in the same pixels). So\, even ignoring Hubble tensions\, this is a very exciting tim e to be involved in extragalactic distance measurements.\n\nAbby used data from JWST to detect the JAGB mode brightness\, which is then the distance indicator of the method. With more telescope time\, and more local calibr ators\, JAGB will only go from strength to strength.\n\nWhen the measured distances are compared to JWST measurements of TRGB and cepheids it has ve ry little scatter with TRGB\, but a little more from cepheids. The ultimat e Hubble parameter is also on the smaller side\, consistent with CMB + ΛC DM and on the border of being inconsistent with SH0ES cepheid+HST based me asurements.\n\nTalk video: youtu.be /mpSsmyInrEA\n\nAbby: abiglee7.g ithub.io\n\nThe paper: arXi v: 2408.03474\n\nAlso see recent\, related Cosmology Talk with Wendy F reedman and Barry Madore at youtu.b e/OkGUoKukwk8\n\n
\n\n[00:00] Intro comments by Shaun\n\n[01:06] Abby's opening comments on paper and CCHP\n\n[01:37] Two takeaways to remember \n\n[02:36] Background and m otivation for this work\n\n[04:50] Asymptotic Giant Branch Stars \, HR diagram\, carbon stars as s tandard candles\n\n[06:38] The J-Region Asymptotic Giant Branch (JAGB) Method\n\n[08:30] History of the JAGB Method\n\ n[17:08] Comparison of brig htnesses between distance indicators\n\n[18:58] The JAGB Method Advantages\n\n[20:25] TRGB\, Cepheids\, and JAGB are ind ependent methods\n\n[22:45] How accurate/precise are JAGB distances vs TRGB and Cepheids?\n\n [25:38] Comments on the pap er\n\n[30:32] How do yo u know where the outer disk is?\n\n[33:32] Final H0 and Distance Comparisons\n\n[37:21] Summary\n\n[37:57] Is JAGB the gold standard method of the future?\n\n[43:36] What current work in cosmology is interesting but underappreciated?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/91/ END:VEVENT BEGIN:VEVENT SUMMARY:Ana Alexandre\, Valentin Thoss (Max Planck Institute for Physics) DTSTART:20240921T060000Z DTEND:20240921T070000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/92 DESCRIPTION:Title: A New Window for PBH Dark Matter (Due to Delayed Hawking Ra diation)?\nby Ana Alexandre\, Valentin Thoss (Max Planck Institute for Physics) as part of Cosmology Talks\n\n\nAbstract\nAna Alexandre and Vale ntin Thoss tell us about their recent papers examining the consequences of a potential "memory burden" effect on decaying primordial blackholes (PBH s). \n\nThis memory burden effect would be a consequence of quantum gravit y and would substantially slow down the Hawking evaporation of blackholes. The consequences for primordial blackholes would be very important becaus e it would open a whole window of PBH masses as dark matter candidates. (M asses that are normally ignored because PBHs of these masses are presumed to have decayed by today.)\n\nAll fundamental physicists would agree that Hawking radiation must breakdown at some point at/before a blackhole reach es the Planck mass. This proposed memory burden effect goes a step further and claims that the breakdown must happen no later than when a blackhole has decayed to half of its original mass. This is not universally agreed u pon\, but it's still worth examining the consequences if it is true.\n\nRe corded video: youtu.be/p8UhnWri4II< /a>\n\nAna: at linkedin
\nValentin: at Max Planck Inst\n\nAna's paper: arXiv: 2402.14069
\nValentin's paper: arXiv: 2402.17823\n\n
\n\n[00:00] Intro comments by Shaun\n\n[01 :30] Brief opening comments by Valentin\n\n[02:18] Two takeaways to remember by Ana\n\n[02:50] Getting into the background\n\n[07:45] Black hole evaporation\; "memory burden" effe ct\n\n[14:32] How well ac cepted is the memory burden effect by experts in its field?\n\n[17:34] New parameter space for PBH DM\n\n[21:06] Big Bang Nucleosynthesis\n\n[22:24] Relaxing constraints with memory burden\n\n[26:51] 4 Constraints (sections 2.5-2.8 in 2402.1782 3)\n\n[27:41] Constraint s from galactic gamma ray emission\n\n[32:22] The other 3 constraints\n\n[37:42] The landscape of constraints\n\n[38:5 3] Combined constraints plot (Fig. 1 in 2402.17823)\n\n[42:18] Discussion re lower bound on the mass\n\n[43:40] Where to next?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/92/ END:VEVENT BEGIN:VEVENT SUMMARY:Daniele Sorini (Durham University) DTSTART:20241113T050000Z DTEND:20241113T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/93 DESCRIPTION:Title: How Dark Energy Affects Past and Future Star Formation\ nby Daniele Sorini (Durham University) as part of Cosmology Talks\n\n\nAbs tract\nDaniele Sorini tells us about his research looking into how the val ue of dark energy affects star formation in the universe. He builds an ana lytic model of star formation in the universe\, which allows him to follow the universe to very late times and ask "if Λ was different\, how many t otal stars could form over the entire history of the universe?"\n\nThis is the crucial question one wants to ask when examining anthropic explanatio ns of Λ scientifically. Previous studies have asked this question using s imulations\, forcing them to stop after a finite amount of time.\n\nFascin atingly\, Daniele finds that there is a value of Λ where star formation p eaks\, which is about 0.1 times the value in our universe. Previous simula tion-based studies maybe didn't spot this because they simply didn't do si mulations with Λ less than our observed value\, except for Λ=0\, but als o they didn't go to late enough times.\n\nWhen combined with a uniform pri or for Λ he finds that our value\, or a value smaller than it still only has a 0.5% chance\, but with other priors one gets other results.\n\nTalk video: youtu.be/cgfV2vwtEgs\n\n The paper: arXiv: 2411.07301\n\nDaniele: danielesorini.com\n\n
\n\nIndex to Key Parts of the Talk\n\n[0:00:00] Intro comments by Shaun\n \n[0:01:13] Brief opening com ments by Daniele\n\n[0:02:09] Sneak preview of the results\n\n[0:05:07] What was surprising about the results?\n\n[0:0 7:24] Motivation and current relevance for this work\n\n[0:15:59] Can ΛCDM explain observations?\n\n[0:27:03] Diff models reach diff conclusions but all posteriors peak at Λ>>Λobs\n\n[0:29:53] Details\n\n[0:36:48] Improved match with observations of cosmic SFR densi ty vs time\n\n[0:39:25] Stellar mass density converges as time tends to infinity\n\n[0:41:18] Star formation saturates a t t>>100 Gyr (Fig 9 in paper)\n\n[0:49:31] Larger Λ -> Fewer massive haloes (Fig 4)\n\n[0:50 :20] Larger Λ -> More effi cient haloes (Fig 8)\n\n[0:55:56] Does Λ=Λobs promote the generation of observers? (Fig 11) \n\n[0:58:14] Conclusions v ery sensitive to prior on Λ (Fig 12)\n\n[1:01:27] Conclusions\n\n[1:09:25] Where to next?\n\n[1:17:20] What current cosmology work is interest ing but underappreciated by the community?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/93/ END:VEVENT BEGIN:VEVENT SUMMARY:Arnaud de Mattia\, Héctor Gil-Marín\, Pauline Zarrouk (DESI Coll aboration) DTSTART:20241120T050000Z DTEND:20241120T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/94 DESCRIPTION:Title: DESI 2024: Cosmology Results from the Power Spectrum's Full Shape\nby Arnaud de Mattia\, Héctor Gil-Marín\, Pauline Zarrouk (DE SI Collaboration) as part of Cosmology Talks\n\n\nAbstract\nArnaud de Matt ia\, Hector Gil-Marín and Pauline Zarrouk tell us about the latest DESI k ey papers. These ones are covering the "full shape" of the galaxy power sp ectrum. This is in contrast to their results from April\, which were centr ed around the Baryon Acoustic Oscillation (BAO) feature.\n\nThe analysis i s an absolute tour de force\, explaining why the video is so long. DESI ha ve done a lot of analysis and it takes a while to unpack. (The raw recordi ng of this video was more than 200 minutes long!)\n\nThe results aren't qu ite so eye-opening as the BAO ones were in April. The evidence for evolvin g dark energy is still there\, but the significance of this evidence hasn' t changed much. They are however able to do a bunch of tests of modified g ravity and find that\, unlike ΛCDM\, General Relativity appears to be in great shape (at least as far as DESI observations are concerned).\n\nWe're properly in the era of Stage 4 cosmology now! Thanks DESI for the wonderf ul analyses and results.\n\nTalk video recording: youtu.be/2mlU-YzEbw\n\nRelevant papers o n the arXiv:
\n2411.12026 - Modified Gravity Constraints from the Full Shape Modeling of Clusterin g Measurements from DESI 2024
\n2411.12025 - Characterization of DESI fiber assignment incompleten ess effect on 2-point clustering and mitigation methods for DR1 analysis\n2411.12024 - Mitigating Imaging Systematics for DESI 2024 Emission Line Galaxies and Beyond
\n 2411.12023 - Exploring HOD- dependent systematics for the DESI 2024 Full-Shape galaxy clustering analy sis
\n2411.12022 - DESI 2024 VII: Cosmological Constraints from the Full-Shape Modeling of Cluster ing Measurements
\n2411.1202 1 - DESI 2024 V: Full-Shape Galaxy Clustering from Galaxies and Quasar s
\n2411.12020 - DESI 20 24 II: Sample Definitions\, Characteristics\, and Two-point Clustering Sta tistics
\n\nArnaud: in spirehep.net/authors/1881382
\nHector: www.ub.edu/bispectrum
\nPauline: inspirehep.net/authors/1884383
\n\nDESI itself: desi.lbl.gov
\n\nTimes tamp links to key parts of the talk:
\n00:00 Intro and brief overview of new results
\n06:12 The background and motivation
\n24:05 Full shape galaxy cl ustering analysis
\n55:46 Systematic effects
\n1:10:10 Cosmology results!< br>\n1: 19:28 Beyond ΛCDM and GR constraints
\n1:37:02 Conclusions and additi onal discussion
\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/94/ END:VEVENT BEGIN:VEVENT SUMMARY:Guadalupe Cañas Herrera\, Hervé Aussel (Euclid Consortium) DTSTART:20250319T050000Z DTEND:20250319T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/95 DESCRIPTION:Title: Euclid 2025: Science Goals and Q1 Data Summary\nby Guad alupe Cañas Herrera\, Hervé Aussel (Euclid Consortium) as part of Cosmol ogy Talks\n\n\nAbstract\nThe day has arrived. The space observatory Euclid is producing and sharing results. In this video Guadalupe Cañas-Herrera and Hervé Aussel tell us about Euclid\, its science goals and the Q1 data set they have released today.\n\nTalk video recording\n\nEuclid Papers\n\nEuclid Consort ium details on the Q1 release\n\nESA details on the Euclid Q1 release \n\n
\n\nIndex to Key Parts of the Talk\n\n[01:18] Euclid overview\n\n[02:21] Euclid: intro and goals\; dark energy\, accelerated expansion\, dark matter\n\n[04:38] Why the name Euclid?\n\n[06:28] Universe timeline\; Euclid targets 0 < z < 3 to study LSS and create 3D map\n\n[08:58] Two probes: cosmic shear and galaxy clustering\n\ n[12:35] Mapping the Univers e in 3D\n\n[13:05] Eucli d spacecraft and instrument details\n\n[18:46] Scope of the Euclid Wide Survey\n\n[19:59] What to Expect\n\n[20:50] Advantages of Euclid as a s pace mission\n\n[22:06] Outlook for constraints on w\\_0 and w\\_a\n\n[23:40] Q1 Data Release Contents\n\n[26:06] The Euclid Deep Fields\n\ n[30:16] Q1 Processing\ n\n[33:32] Photometric Reds hifts and Photometric Classification\n\n[34:55] Physical Parameters\n\n[36:31] NISP Spectroscopy\n\n[40:16] SPE Redshifts Measurements\n\n[ 47:13] Important Caveats\n\n[50:54] Conclusion \n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/95/ END:VEVENT BEGIN:VEVENT SUMMARY:Teresa Matamoro\, Mike Walmsley\, Phil Holloway (Euclid Consortium ) DTSTART:20250319T050000Z DTEND:20250319T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/96 DESCRIPTION:Title: Euclid 2025: AGN\, Galaxy Morphology & Strong Lensing\n by Teresa Matamoro\, Mike Walmsley\, Phil Holloway (Euclid Consortium) as part of Cosmology Talks\n\n\nAbstract\nTeresa Matamoro\, Mike Walmsley and Phil Holloway tell us about three key areas Euclid has shed a scientific light on in their Q1 data release today. These are active galactic nuclei\ , galaxy morphology and strong lensing.\n\nTalk video recording\n\nEuclid Papers\n\nEucli d Consortium details on the Q1 release\n\nESA details on the Euclid Q1 re lease\n\nPapers:\n\n[2503.15326] Euclid Quick Data Release (Q1). The Strong Lensing Discovery Engine C - Finding lenses with machine learning\n\n[2503.15324] Euclid Quick Data Release ( Q1): The Strong Lensing Discovery Engine A -- System overview and lens cat alogue\n\n[2503.15320] Eucl id Quick Data Release (Q1). The active galaxies of Euclid\n\n[2502.06505] Euclid: A complete Einstein ring in NGC 6505\n\n[2404. 02973] Scaling Laws for Galaxy Images\n\n
\n\nTimestamp Index to Key Parts of the Talk\n\n[00:00:00] Shaun's intro\n\n[00:01:03] AGN overview (Teresa)\n\n[00:05:47] New results and main takeaways\n\n[00:09:43] Building a multi-wavelength catalogue\n\n[00:13:54] Colour-colour selections\n\n[00:17:31] Spectroscopy\n\n[00:18:51] SED fitting\n\n[00:20:32] Other AGN works\n\n[00:21:22] What next?\n\n[00:22:38] Application to cosmology (Mike)\n\n[0 0:23:44] Galaxy morphology< /a>\n\n[00:31:34] What are foundation models?\n\n[00:38:08] Strong lensing (Phil)\n\n[00:42:01] 497 strong lenses found in Euclid Q1\n\n[00:44: 29] Euclid will revolutioni se strong lensing\n\n[00:47:33] The Euclid Strong Lensing Discovery Engine\n\n[00:54:43:] Which lenses did we find?\ n\n[00:57:28] Notable lens candidates\n\n[01:02:49] With 100k future strong lenses\, any possibility of GR tests?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/96/ END:VEVENT BEGIN:VEVENT SUMMARY:Cristhian Garcia Quintero\, Paul Martini (DESI Collaboration) DTSTART:20250319T050000Z DTEND:20250319T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/97 DESCRIPTION:Title: Cosmology Results from DESI DR2 BAO\nby Cristhian Garci a Quintero\, Paul Martini (DESI Collaboration) as part of Cosmology Talks\ n\n\nAbstract\nCristhian Garcia Quintero and Paul Martini tell us about th e baryon acoustic oscillation measurements in data release two (DR2) of th e Dark Energy Spectroscopic Instrument (three years of data). As with the first data release they are seeing evidence for evolving dark energy. They now see it when combining with just CMB\, or with "just" Dark Energy Surv ey supernovae and clustering data.\n\nTalk Recording: youtube.com/watch?v=YiRaDtslycE\n\nC risthian Garcia Quintero: gqcrist hian.github.io\n\nPaul Martini: OSU.edu\n\nGuide to DESI DR2 Results\, dated 19-M ar-2025\n\nRelevant papers on the arXiv:\n\n[2503.14738] DESI DR2 Results II: Measurements of Baryon Acoustic Oscillations and Cosmological Constraints\n\n[2503.14739] DESI DR2 Results I: Baryon Acousti c Oscillations from the Lyman Alpha Forest\n\n[2503.14741] Validation of the DESI DR2 Ly$α$ BAO anal ysis using synthetic datasets\n\n[2503.14742] Validation of the DESI DR2 Measurements of Baryon Acous tic Oscillations from Galaxies and Quasars\n\n[2503.14743] Extended Dark Energy analysis using DESI D R2 BAO measurements\n\n[250 3.14744] Constraints on Neutrino Physics from DESI DR2 BAO and DR1 Full Sh ape\n\n
\n\nTimestamp Index to Key Parts of the Talk\n\n[00: 00:00] Shaun's intro\n\n[0 0:00:54] Overview of findings \n\n[00:02:53] Main plot of results with and w/o supernova datasets\n\n[00:03:46] The highest significance plot and the ro le of DES Y5 data\n\n[00:04:40] w0wa parameterization vs physical models beyond LCDM\n\n[00:07 :55] Getting deeper into th e background\n\n[00:09:14] The BAO scale as a "standard ruler"\n\n[00:14:00] Mystery of Cosmic Acceleration slide\n\n[ 00:15:18] Getting into detai ls of BAO measurements from DESI DR2\n\n[00:17:10] Transition from DESI DR1 to DR2\n\n[00:18: 43] DESI Data Release 2 \n\n[00:20:13] Correlation function measurements\n\n[00:28:16] DESI LyA Measurement\n\n[00:32:50] DESI LyA BAO Measurement\n\n[00:38:59] Cosmological constraints under LCD M\n\n[00:50:33] Omega_m under w0waCDM\n\n[00:51:25] Constraints on evolving dark energy\n\n[00:58:45] Robustness of the DE results\n\n[01:03:3 8] Binning the DE equation o f state\n\n[01:06:50] DE SI and neutrino mass\n\n[01:11:00] Future outlook\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/97/ END:VEVENT BEGIN:VEVENT SUMMARY:Wright\, Stölzner\, Reischke\, Asgari\, Kuijken (Kilo-Degree Surv ey (KiDS)) DTSTART:20250326T050000Z DTEND:20250326T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/98 DESCRIPTION:Title: KiDS­ Legacy - The Final Cosmology Results\nby Wright\ , Stölzner\, Reischke\, Asgari\, Kuijken (Kilo-Degree Survey (KiDS)) as p art of Cosmology Talks\n\n\nAbstract\nAngus Wright\, Benjamin Stölzner\, Robert Reischke\, Marika Asgari and Konrad Kuijken tell us about the final cosmology results from the Kilo Degree Survey (KiDS-Legacy). After exhaus tive improvement of their analysis\, and consistency tests\, and a six mon th wander in the B-Mode wilderness they emerge with no S8 tension at all.\ n\nTalk Video Recording: youtu.be/P IQKe-tW1xQ\n\nAngus: anguswri ght.github.io\n\nBenjamin: inspirehep.net/authors/1944983\n\nRobert: inspirehep.net/authors/2219647\n\nMarika: < a href="https://www.ncl.ac.uk/maths-physics/people/profile/marikaasgari.ht ml">ncl.ac.uk/...\n\nKonrad: universiteitleiden.nl/...\n\n Papers:\n\n2503.19442\n \n2503.19441\n\n2503.19440\n\n
\n\nIndex to Key Parts of Talk\n\n[00:00:00] Shaun's intro\n\n[00:01:00] Overview and main cosmological constraints\n\n[00:04:11] Internal Consistency Constraints \n\n[00:05:15] The early vs late debate\n\n[00:07:20] Blueprint for Stage-IV\; Why now? Why not sooner?\n\n[00:10:26] Since 2021: Updated calibrations \, samples\, and area\n\n[00:20:00] Details of KiDS Legacy analysis: Redshift Calibration\n\n [00:27:43] Covariance and m odelling\n\n[00:33:51] Updated Astrometric Calibration\n\n[00:36:17] B-modes issue\n\n[00:43:05] Internal Consistency\n\n[00:54:20] Consistency motivates further join t analyses\n\n[01:00:21] What's next? Onwards to Stage-IV\n\n[01:02:23] What's underappreciated by the community in curr ent cosmology work?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/98/ END:VEVENT BEGIN:VEVENT SUMMARY:Sankarshana Srinivasan (Ludwig-Maximilians Universitat) DTSTART:20251107T050000Z DTEND:20251107T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/99 DESCRIPTION:Title: Cosmological Gravity on All Scales\nby Sankarshana Srin ivasan (Ludwig-Maximilians Universitat) as part of Cosmology Talks\n\n\nAb stract\nSankarshana Srinivasan tells us about his work building the framew ork to constrain (or detect!) modified gravity using upcoming surveys. Bui lding on earlier work developing model independent modified gravity simula tions\, Shankar now shows how a clever transform (the BNT transform) is ab le to better isolate the weak-lensing kernel\, meaning one can more cleanl y cut out the fully messy non-linear scales without losing too much usable information. We're all looking forward to the talk in 3-5 years' time app lying these methods to Euclid and LSST data!\n\nPaper: arXiv: 2409.06569\n\nTalk video: youtube.com/watch?v=nIdCpcObSVU\n\nCosmology Talk on earlier work in this series by Dan Thomas: The first model independent cosmological simulations of modified gravity\n\nIndex to Key Parts of the Talk\n\nShaun's in tro\n\nShankar's brief ov erview on the paper\n\nA key insight: mitigating baryonic feedback\n\nA physical intuition on mu μ and eta η parameters< /a>\n\nBinning strategies\n\nSome Problems with ΛCD M\n\nVast model space\n\nPost-Friedmann Formali sm: Pixelized Poisson Equation\n\nN-body simulations: Measuring P(k) for binned μ\n\nN-body simulations: ReACT for binn ed μ\n\nN-body simulat ions: Computing 3x2pt observables\n\nFisher Forecasts\n\nFisher Forecasts: Key questions\n\nThe Bernardeau-Nimishi-Taruya (BNT) Transform\n \nMitigating Baryonic Feedb ack\n\nWhere does the c onstraining power come from?\n\nAdding the concentration fit\n\nWhat next?\n\nSummary slide points (but no discussion)\n\nWhat current work in cosmology is interestin g but underappreciated?\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/99/ END:VEVENT BEGIN:VEVENT SUMMARY:Miguel Zumalacarregui (Max Planck Institute for Gravitational Phy sics) DTSTART:20260126T050000Z DTEND:20260126T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/100 DESCRIPTION:Title: A magnified and diffracted black hole merger (GW231123)\nby Miguel Zumalacarregui (Max Planck Institute for Gravitational Physi cs) as part of Cosmology Talks\n\n\nAbstract\nCan gravitational waves get gravitationally lensed? The first ever detection of this might have just h appened. This is especially cool because if we could routinely measure len sing of gravitational waves\, we could use that to measure all sorts of ot her important things like the Hubble constant and precision tests of gravi ty to name just two. One of the interesting things you will hear about in today's talk is an improved modeling of the candidate lens. This better na ils down the probability that the wave really was lensed and even more fun gives insight into what astrophysical things the source and lens could be . In today's talk\, we're joined by Miguel Zumalacarregui from the Max Pla nk Institute for Gravitational Physics in Potsdam\, Germany his new paper. \n\nVideo recording: youtube.com/watch?v=ZGqOpDTL8k4\n\nMiguel: miguelzuma.github.io\n\nPaper: arXiv: 2512.17631\n\nLigo-Virgo-Kagra analysis: arXiv: 2512.16347\n\n
\n\nIndex to Key Parts of the Talk\n\n[0:00:00] Shaun's intro\; potential new w ay to measure H0 and test gravity
\n\n[0:00:54] Miguel's overview on paper and so me things it now allows doing
\n\n[0:02:25] Quick intro to the results\; statist ical analysis supports the lensing hypothesis\; non-symmetric lens
\n\n[0:05:26] Is there anything confusing about these results?
\n\n[0:06:26] Background and m otivation for this research
\n\n[0:11:15] Why lensing analysis can be done with gravitational waves
\n\n[0:13:05] Error bars on the parameters
\n\n[0:14:17] Journey o f a lensed gravitational wave
\n\n[0:19:22] Predicting and extracting these sig nals\; Wave-optics lensing
\n\n[0:21:58] Frequency evolution
\n\n[0:26:39] How diffe rent is a lensed one from unlensed one with different mass?
\n\n[0:27:17] Lens model\; Point lens + external potential
\n\n[0:34:22] GW231123 Bayesian analysi s\; 3 models
\n\n[0:41:04] Caveat: bias factors
\n\n[0:48:07] Resolution of unlensed analysis inconsistencies between different models
\n\n[0:51:02] Surprising fea ture: sky localization is much wider for the lensing analysis
\n\n< a href="https://www.youtube.com/watch?v=ZGqOpDTL8k46t=3287s">[0:54:47] Mic rolens properties
\n\n[0:58:03] What is the microlens? (IMBH\, stellar cluster\ , DM object\, etc?)
\n\n[1:02:44] Additional macro-images?
\n\n[1:05:51] Where to ne xt? Outlook: Additional lensing signatures
\n\n[1:10:17] Outlook: discover sour ces beyond the detector horizon
\n\n[1:11:27] Another twist: lensing multi-mess enger delections
\n\n[1:12:46] Conclusions
\n\n[1:14:04] Particularly interesting co smology work that's underappreciated by the community
\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/100/ END:VEVENT BEGIN:VEVENT SUMMARY:Jessie Muir\, Juan Mena-Fernández\, Santiago Avila\, Maria Vincen zi (Dark Energy Survey Collaboration) DTSTART:20260204T050000Z DTEND:20260204T060000Z DTSTAMP:20260404T110824Z UID:CosmologyTalks/101 DESCRIPTION:Title: Dark Energy Survey - Combined cosmology from BAO + SN (+CM B)\nby Jessie Muir\, Juan Mena-Fernández\, Santiago Avila\, Maria Vin cenzi (Dark Energy Survey Collaboration) as part of Cosmology Talks\n\n\nA bstract\nFour members of the Dark Energy Survey Collaboration discuss the latest findings. This talk is based on these two papers on the arXiv:\n\n( 1) Main talk content: [2503.067 12] Dark Energy Survey: implications for cosmological expansion models fro m the final DES Baryon Acoustic Oscillation and Supernova data\n\n(2) Newly released paper: [2601.148 64] Dark Energy Survey: DESI-Independent Angular BAO Measurement\n\nAb out the authors: Jessie Muir\, < a href="https://inspirehep.net/authors/2011410">Juan Mena-Fernández\, Santiago Avila\, Maria Vincenzi\n\n
\n\n< b>Index to Key Parts of the Talk\n\n[0:00:00] Shaun's intro\n\n[0:01:16] Overview of findings\n\n[0:02:40] How independent is this from DESI?\n\n [0:03:38] Anything particula rly surprising from the analysis?\n\n[0:04:15] Tensions in simpler models\, data reconciled with w 0waCDM\n\n[0:08:40] SN I a and BAO as distance probes\n\n[0:10:17] The Dark Energy Survey (photometric)\n\n[0:11:43] 4 probes: SN Ia\, BAO\, WL + G C\, GC counts\n\n[0:12:2 5] 2024: Λ's annus horribilis\n\n[0:15:08] The DES SN Y5 sample\n\n[0:19:15] DES SN Systematics\n\n[0:22:37] DES Y6 BAO\n\n[0:30:58] Galaxy clustering: BAO signal \n\n[0:35:32] Combining SN and BAO: expansion history model\n\n[0:38:11] DES BAO + SN + ΛCDM + θₛ: tensions\n\n[0:41:00] Curvature: kΛCDM\ n\n[0:45:25] DES expansion models: wCDM and w0waCDM\n\n[0:54:24] Hubble tension is not resolved\n\n[1:02:38] Results in νΛCDM\n\n[1:06:07] Where to next? Future of DES< /a>\n\n[1:07:50] Future of BAO\n\n[1:09:22] Future of SN\n\n[1:12:55] Wha t current cosmology work is underappreciated by the community?\n\n[1:13:40] Impact of DES SN-Dove kie\n LOCATION:https://stable.researchseminars.org/talk/CosmologyTalks/101/ END:VEVENT END:VCALENDAR