BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Aron Kovacs (DAMPT\, University of Cambridge) DTSTART:20200618T140000Z DTEND:20200618T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/1 DESCRIPTION:Title: Well-posed formulation of scalar-tensor ef fective field theory\nby Aron Kovacs (DAMPT\, University of Cambridge) as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Jorge Bellorin (Universidad de Antofagasta) DTSTART:20200625T140000Z DTEND:20200625T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/2 DESCRIPTION:Title: Horava gravity in canonical formalism\ nby Jorge Bellorin (Universidad de Antofagasta) as part of Gravity @ SISSA \n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Xisco Jimenez (Max Planck Institute for Gravitational Physics) DTSTART:20200702T130000Z DTEND:20200702T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/3 DESCRIPTION:Title: Ringdown overtones\, black hole spectrosco py\, and no-hair theorem tests with overtones and angular modes\nby Xi sco Jimenez (Max Planck Institute for Gravitational Physics) as part of Gr avity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/3/ END:VEVENT BEGIN:VEVENT SUMMARY:Luis Lenher (Perimeter Institute for Theoretical Physics) DTSTART:20200709T140000Z DTEND:20200709T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/4 DESCRIPTION:Title: Extensions to GR: Roadblocks & potential w ay through\nby Luis Lenher (Perimeter Institute for Theoretical Physic s) as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Pantelis Pnigouras (Mathematical Sciences and STAG Research Centre \,University of Southampton\, Southampton\, UK) DTSTART:20200716T140000Z DTEND:20200716T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/5 DESCRIPTION:Title: Secular instabilities in neutron stars \nby Pantelis Pnigouras (Mathematical Sciences and STAG Research Centre\,U niversity of Southampton\, Southampton\, UK) as part of Gravity @ SISSA\n\ n\nAbstract\nAs opposed to dynamical instabilities\, secular instabilities describe the slow exponential growth of a perturbation\, due to the prese nce of a dissipation mechanism. We will see how they are related to an old problem\, regarding the shape of the Earth\, and briefly review their man ifestation in neutron stars. We will focus on the secular instability driv en by the emission of gravitational waves\, which can be used to derive in formation about the largely unknown neutron star interior composition\, as well as provide an explanation for some long-standing problems of pulsar observations. Finally\, we will present a recently reported study\, accord ing to which this instability affects the evolution of neutron star binari es\, thus becoming potentially relevant for gravitational-wave detections. \n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Alberto Sesana (University of Milan-Bicocca) DTSTART:20200911T140000Z DTEND:20200911T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/6 DESCRIPTION:Title: Supermassive black hole astrophysics with pulsar timing arrays\nby Alberto Sesana (University of Milan-Bicocca) as part of Gravity @ SISSA\n\n\nAbstract\nThe detection of gravitational w aves (GWs) is shaping our understanding of the Universe. At nHz frequencie s\, pulsar timing arrays (PTAs) promise to detect the signal coming from t he cosmological population of supermassive black hole binaries (SMBHBs) wi thin the next few years. After reviewing the astrophysics of SMBHBs\, I wi ll describe the current status of the PTA effort\, present the most recent limits\, and their astrophysical implications.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Katsuki Aoki (Waseda University) DTSTART:20200924T093000Z DTEND:20200924T103000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/7 DESCRIPTION:Title: Gravitational positivity bounds\nby Ka tsuki Aoki (Waseda University) as part of Gravity @ SISSA\n\n\nAbstract\nT he desired properties of scattering amplitudes such as unitarity yield non -trivial constraints on low energy effective field theories (EFT)\, called positivity bounds. The bounds are clearly derived when gravity is ignored while their extensions to include gravity are not straightforward due to a divergence coming from the graviton t-channel exchange. We study the val idity of positivity bounds in the presence of a massless graviton\, assumi ng the Regge behavior of the amplitude. Under this assumption\, the proble matic t-channel pole is canceled with the UV integral of the imaginary par t of the amplitude in the dispersion relation\, which gives rise to finite corrections to the positivity bounds. We find that low-energy EFT with "w rong" sign are generically allowed. The allowed amount of the positivity v iolation is determined by the Regge behavior. This violation is suppressed by $M_{\\rm pl}^{-2} \\alpha'$ where $\\alpha'$ is the scale of Reggeizat ion. This implies that the positivity bounds can be applied only when the cutoff scale of EFT is much lower than the scale of Reggeization. We then obtain the positivity bounds on scalar-tensor EFT at one-loop level. Impli cations of our results on the degenerate higher-order scalar-tensor (DHOST ) theory are also discussed.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/7/ END:VEVENT BEGIN:VEVENT SUMMARY:Clare Burrage (University of Nottingham) DTSTART:20201001T140000Z DTEND:20201001T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/8 DESCRIPTION:Title: Screening of fifth forces in scalar tensor theories\nby Clare Burrage (University of Nottingham) as part of Grav ity @ SISSA\n\n\nAbstract\nScalar tensor theories are of interest as possi ble explanations for the acceleration of the expansion of the universe\, a nd also as a way to understand possible modifications of gravity. However\ , it is always necessary to explain why\, if such a theory describes our u niverse\, a scalar mediated fifth force has not been seen. I will discuss two possible explanations for this: (1) that the underlying physical theor y is scale invariant and (2) that non-linearities in the theory act to sup press\, or 'screen' the fifth force. I will focus\, in particular\, on th e challenges encounter when trying to embed these mechanisms in effective field theories.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Raissa F. P. Mendes (Universidade Federal Fluminense) DTSTART:20201015T140000Z DTEND:20201015T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/9 DESCRIPTION:Title: Neutron stars and screening mechanisms \nby Raissa F. P. Mendes (Universidade Federal Fluminense) as part of Grav ity @ SISSA\n\n\nAbstract\nScalar-tensor theories of gravity offer an inte resting framework for cosmology\, since the new scalar degree of freedom\, when active at the largest scales in the Universe\, could help to drive i ts accelerated expansion. At the same time\, the scalar field must conceal its effects in solar system scales\, where observations conform extremely well to general relativity. Such screening of the scalar fifth force is o ften density-dependent\, and models are usually tuned to general relativit y for solar system densities and higher. In this seminar we explore the po ssibility that screening may actually fail when densities are the highest\ , namely\, in the core of the most compact neutron stars found in nature. We discuss the necessary microphysical requirements for the nuclear equati on of state\, as well as some properties of neutron stars with unscreened cores in a few interesting models.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Daniele Viganò (Institute of Space Science CSIC) DTSTART:20201008T140000Z DTEND:20201008T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/10 DESCRIPTION:Title: Turbulent dynamos in binary neutron star mergers\nby Daniele Viganò (Institute of Space Science CSIC) as part of Gravity @ SISSA\n\n\nAbstract\nOne of the most important open issue in the theoretical understanding of binary neutron star mergers is the amplif ication of magnetic fields. This happens first in a turbulent way at small scales via Kelvin-Helmholtz instability\, and with a large-scale ordering via winding and magneto-rotational instability after. However\, the numer ical resolution currently doable with the most expensive simulations (tens of millions of CPU hours) is very far from capturing the scales at play ( possibly\, fractions of meters). Here we present how a sub-grid-scale mode ling of the non-resolvable dynamics can reproduce a magnetic amplification up to local values of 10^17 G at a much lower computational cost\, during the first 10 milliseconds after the merger. Implications for large-scale structures and jet formation (gamma-ray burst) are discussed.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/10/ END:VEVENT BEGIN:VEVENT SUMMARY:Arthur G. Suvorov (University of Tübingen) DTSTART:20201029T150000Z DTEND:20201029T160000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/11 DESCRIPTION:Title: Building a theory around a given spacetim e\nby Arthur G. Suvorov (University of Tübingen) as part of Gravity @ SISSA\n\n\nAbstract\nA validation of non-Kerr parameters in astrophysical data concerning black holes would provide compelling evidence for the b reak-down of general relativity in the strong-field regime. Suppose we fo und that some non-Kerr metric describes black holes\; is there a clear wa y that this can be used to guide us towards the "true" theory of gravity? While a full answer to this problem is still far away\, some recent prog ress has been made in that an explicit solution to the inverse problem is found: given a metric\, reconstructed from astrophysical data\, it is sh own how a theory can be built around it. The overarching family of theori es reduces to a number of well known cases in some limits\, including sca lar-tensor\, f(R)\, and k-essence theories. Some implications of this fin ding and other recent works are discussed.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/11/ END:VEVENT BEGIN:VEVENT SUMMARY:Claudia de Rham (Imperial College London) DTSTART:20201119T100000Z DTEND:20201119T110000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/12 DESCRIPTION:Title: Causality in Curved Spacetimes\nby Cl audia de Rham (Imperial College London) as part of Gravity @ SISSA\n\n\nAb stract\nI will investigate the propagation of gravitational waves on curve d spacetimes within the low energy effective field theory of gravity\, whe re effects from heavy fields are captured by higher dimensional curvature operators. I will clarify why a mild level of superluminality is not in co ntradiction with causality\, analyticity or Lorentz invariance and show ho w consistent gravitational low energy effective theories can self-protect by ensuring that any time advance and superluminality calculated within th e regime of validity of the effective theory is necessarily unresolvable f or such theories. These considerations are particularly relevant for putti ng constraints on cosmological and gravitational effective field theories and I will provide explicit criteria to be satisfied so as to ensure causa lity.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Sergey Sibiryakov (Perimeter Institute for Theoretical Physics) DTSTART:20201106T130000Z DTEND:20201106T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/13 DESCRIPTION:Title: Quantum gravity with anisotropic scaling: Past\, Present\, Future\nby Sergey Sibiryakov (Perimeter Institute fo r Theoretical Physics) as part of Gravity @ SISSA\n\n\nAbstract\nI will re view the status of gravity with anisotropic scaling — an approach to qua ntum gravity proposed in 2009 by P. Horava and necessitating rejection of the Lorentz invariance as a fundamental symmetry of nature at high energie s. During the last decade this proposal has passed the scrutiny of self-co nsistency and phenomenological viability and was put on firm grounds by th e proof that it leads to unitary renormalizable gravity theories. Investig ations in lower dimensions have identified ultraviolet complete asymptotic ally free gravity models\, with preliminary studies indicating that these may also exist in four dimensions. I will discuss phenomenological challen ges to this program and give an outlook of future directions.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/13/ END:VEVENT BEGIN:VEVENT SUMMARY:Jose Maria Ezquiaga (University of Chicago) DTSTART:20201022T140000Z DTEND:20201022T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/14 DESCRIPTION:Title: Cosmology and fundamental physics with bi nary black-hole mergers\nby Jose Maria Ezquiaga (University of Chicago ) as part of Gravity @ SISSA\n\n\nAbstract\nGravitational waves (GWs) from the first two observing runs of LIGO/Virgo have uncovered a population of stellar-mass binary black holes (BBHs). In the first part of the talk\, I will discuss the consistency of these observations with the theory of pai r instability supernova (PISN)\, which predicts a mass gap in the black-ho le mass spectrum in the range ~50 -120 Msun. I will then concentrate on th e prospects of detecting BBHs above the PISN gap. These "far side of the P ISN gap" binaries would be ideal multi-band GW sources with promising scie nce. I will show how far-side binaries can become standard sirens\, leave imprints in the stochastic GW background and might help constraining nucle ar reaction rates. In the second part of the talk\, I will discuss the pos sibility of identifying lensed GWs from BBHs. In particular\, I will focus on the key role of lensing phase shifts. Contrary to electromagnetic radi ation intuition\, lensing phase shifts could distort the GW waveform so th at it differs from the (unlensed) general relativity prediction. I will qu antify how relevant these distortions are for current GW detectors and sig nals\, outlining an optimal lensing search strategy. Time permitting\, I w ill discuss tests of general relativity with lensed and unlensed GW events .\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/14/ END:VEVENT BEGIN:VEVENT SUMMARY:Diego Blas (King's College London) DTSTART:20201112T100000Z DTEND:20201112T110000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/15 DESCRIPTION:Title: Quenching or detecting BH rotational supe rradiances\nby Diego Blas (King's College London) as part of Gravity @ SISSA\n\n\nAbstract\nIn this talk I’ll discuss two recent results on BH superradiance: first\, I will describe how BH photon superradiance is typ ically quenched by interactions of the photon cloud with the ambient elect rons. Second\, I will explain how an axionic cloud may impact the CMB if i t decays into low energy photons which quickly heat and ionise the surroun ding medium to Mpc scales.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/15/ END:VEVENT BEGIN:VEVENT SUMMARY:Andrea Maselli (La Sapienza University) DTSTART:20201126T130000Z DTEND:20201126T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/16 DESCRIPTION:Title: Extreme mass ratio inspirals as probes of scalar fields\nby Andrea Maselli (La Sapienza University) as part of Gravity @ SISSA\n\n\nAbstract\nTesting the nature of gravity and the valid ity of Einstein's\ntheory in the strong field regime is one of the most am bitious\ngoals of gravitational wave (GW) detectors\, and a primary target \nfor the space satellite LISA.\n\nAmong binary sources observables by LIS A\, extreme mass ratio inspirals\n(EMRIs) in which a stellar mass object f ollows hundreds of thousands\nof orbits around a supermassive black hole\, harbour the potential for\nvery precise tests of gravity.\n\nThis simples t modifications of General Relativity (GR) predict the\nexistence of scala r fields which modify the gravitational interaction.\nHowever modelling EM RIs and their GW emission beyond GR is a\nmajor challenge\, so far slowed down by the mathematical complexity\nof the problem.\n\nIn this talk I wil l present a new study\, showing that for a vast\nclass of gravity theories \, alternative to GR\, the description of\nEMRIs greatly simplifies\, redu cing the problem to the motion of a\nscalar charge around a Kerr black hol e. In particular I will show\nhow all the information on the GR modificati ons are universally\ncaptured by a single parameter\, the scalar charge of the small\nobject. This promises drastic simplifications in terms of wave form\nmodelling\, and offers the opportunity to use EMRIs for agnostic tes ts\nof General Relativity\, which are independent from the\nunderlying the ory of gravity.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/16/ END:VEVENT BEGIN:VEVENT SUMMARY:Lorenzo Annulli (Instituto Superiore Tecnico CENTRA) DTSTART:20201210T130000Z DTEND:20201210T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/17 DESCRIPTION:Title: Stirred and shaken: dynamical behavior of boson stars and dark matter cores\nby Lorenzo Annulli (Instituto Supe riore Tecnico CENTRA) as part of Gravity @ SISSA\n\n\nAbstract\nThe nature and properties of dark matter are arguably among the most important open issues in science. Interesting candidates for dark matter include light bo sonic fields. Such scalar fields can give rise to confined structures\, as boson stars or Q-balls. Boson stars are interesting hypothetical new "dar k matter stars"\, but also good descriptions of dark matter haloes when th e fields are ultralight. In this talk\, I'm going to focus on the dynamica l response of Newtonian bosonic structures when excited by external matter (stars\, planets or black holes) in their vicinities. The study of the dy namics of such bodies is important for a number of reasons\, ranging from stability to the way they interact with surrounding objects (stars\, plane ts or black holes etc.). Among others issues\, I am going to describe the local changes in the density of a dark matter halo triggered by the presen ce of a massive black hole or a star\, the drag exerted by the bosonic clu mp on stars moving within it\, the flux of energy and momentum induced by coalescing binaries\, etc. I will provide a complete picture of the intera ction between black holes or stars and the ultralight dark matter environm ent they live in.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/17/ END:VEVENT BEGIN:VEVENT SUMMARY:Eugeny Babichev (Laboratoire de Physique Théorique d’Orsay (LPT )) DTSTART:20201203T100000Z DTEND:20201203T110000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/18 DESCRIPTION:Title: Disforming the Kerr metric\nby Eugeny Babichev (Laboratoire de Physique Théorique d’Orsay (LPT)) as part of Gravity @ SISSA\n\n\nAbstract\nI will present a disformal versions of the Kerr spacetime in higher order scalar tensor theories. While the disformed metric has only a ring singularity and asymptotically is quite similar to Kerr\, it is neither Ricci flat nor circular. Non-circularity has far rea ching consequences on the structure of the solution. I will discuss proper ties of three different hypersurfaces in the disformed Kerr metric: the er gosphere\, the stationary limit of infalling observers\, and the event hor izon\, as compared to the Kerr metric.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/18/ END:VEVENT BEGIN:VEVENT SUMMARY:Maria Okounkova (Center for Computational Astrophysics\, Flatiron Institute) DTSTART:20201217T140000Z DTEND:20201217T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/19 DESCRIPTION:Title: Binary Black Hole Mergers beyond General Relativity\nby Maria Okounkova (Center for Computational Astrophysics\ , Flatiron Institute) as part of Gravity @ SISSA\n\n\nAbstract\nAt some le ngth scale\, Einstein's theory of general relativity (GR) must break down and be reconciled with quantum mechanics in a quantum theory of gravity. B inary black hole mergers probe the strong field\, non-linear\, highly dyna mical regime of gravity\, and thus gravitational waves from these systems could contain beyond-GR signatures. While LIGO presently performs model-in dependent and parametrized tests of GR\, in order to perform model-depende nt tests\, we must have access to numerical relativity binary black hole w aveform predictions in beyond-GR theories through full inspiral\, merger\, and ringdown. In this talk\, I will discuss our results in producing full numerical relativity waveforms in beyond-GR theories\, including dynamica l Chern-Simons gravity and Einstein dilaton Gauss-Bonnet gravity.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/19/ END:VEVENT BEGIN:VEVENT SUMMARY:Christian Wuthrich (University of Geneva) DTSTART:20210114T130000Z DTEND:20210114T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/20 DESCRIPTION:Title: Beyond the limits of analogue experiments \nby Christian Wuthrich (University of Geneva) as part of Gravity @ SI SSA\n\n\nAbstract\nAnalogue experiments have attracted interest for their potential to shed light on inaccessible domains. For instance\, ‘dumb ho les’ in fluids and Bose–Einstein condensates\, as analogues of black h oles\, have been promoted as means of confirming the existence of Hawking radiation in real black holes. Contra recent claims in the literature\, I have argued with Karen Crowther and Niels Linnemann (forthcoming) that ana logue experiments are not capable of confirming the existence of particula r phenomena in inaccessible target systems such as astrophysical black hol es. The reason for this is that confirmation through analogue experiments suffers from a form of circularity: they must assume the physical adequacy of the modelling framework used to describe the inaccessible target syste m when it is precisely this adequacy that is at stake. Evans and Thébault (2020) have very recently identified four problems with our argument. I w ill discuss and hopefully rebut their points\, but also constructively dis cuss the similarity of the case of Hawking radiation with that of stellar nucleosynthesis.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/20/ END:VEVENT BEGIN:VEVENT SUMMARY:Alejandro Cárdenas-Avendaño (Illinois Center for Advanced Studie s of the Universe (iCASU)) DTSTART:20210107T130000Z DTEND:20210107T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/21 DESCRIPTION:Title: Experimental gravity with electromagnetic and gravitational waves\nby Alejandro Cárdenas-Avendaño (Illinois C enter for Advanced Studies of the Universe (iCASU)) as part of Gravity @ S ISSA\n\n\nAbstract\nOver the past years\, electromagnetic and gravitationa l observations have been used to understand the nature of black holes and the material around them. Our ability to learn about the underlying physic s\, however\, depends heavily on our understanding of the gravity theory t hat describes the geometry around these compact objects\, and for the elec tromagnetic observations\, also on the complex astrophysics that produces the observed radiation. In this talk\, I will discuss our current ability to constrain and detect deviations from general relativity using (i) the e lectromagnetic radiation emitted by an accretion disk around a black hole\ , and (ii) the gravitational waves produced when comparable-mass black hol es collide\, and when a small compact object falls into a supermassive one in an extreme mass-ratio inspiral. I will also compare the constraining c apabilities of these two types of observations to show how current gravita tional wave observations have already placed constraints on possible modif ications to general relativity\, that are more stringent than what can be achieved with current and near-future electromagnetic observations.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/21/ END:VEVENT BEGIN:VEVENT SUMMARY:Frank Ohme (Max Planck Institute) DTSTART:20210121T100000Z DTEND:20210121T110000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/22 DESCRIPTION:Title: The Binary Universe In Gravitational Wave s\nby Frank Ohme (Max Planck Institute) as part of Gravity @ SISSA\n\n \nAbstract\nThe data of two and a half observing runs of the gravitational -wave interferometers LIGO and Virgo have been fully analyzed to date. The results have recently been published in the second transient catalogue\, GWTC-2\, which contains no fewer than 50 binary merger candidates\, the ma jority of which are expected to be real astrophysical events. Apart from t he shear number of events\, the most recent observations have added some e xciting binaries that further push the boundaries of what we have observed . In this talk\, I will summarize these most recent findings\, highlightin g binaries that are exceptional from an astrophysical or fundamental physi cs point of view. In addition\, statistical methods become more powerful i n extracting properties of the binary population that becomes more and mor e visible in the gravitational-wave universe.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/22/ END:VEVENT BEGIN:VEVENT SUMMARY:Elisa Maggio (Sapienza University of Rome) DTSTART:20210211T130000Z DTEND:20210211T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/23 DESCRIPTION:Title: How does a dark compact object ringdown?< /a>\nby Elisa Maggio (Sapienza University of Rome) as part of Gravity @ SI SSA\n\n\nAbstract\nGravitational waves from the coalescence of compact bin aries provide a unique opportunity to test gravity in strong field regime. In particular\, the postmerger phase of the gravitational signal is a pro xy for the nature of the remnant.\nThis is of particular interest in view of some quantum-gravity models which predict the existence of horizonless compact objects that overcome the paradoxes associated to black holes. Suc h dark compact objects can emit a modified ringdown with respect to the bl ack hole case and late-time gravitational wave echoes as characteristic fi ngerprints.\nIn this talk\, I develop a generic framework to the study of the ringdown of dark compact objects and I assess their detectability with current and future gravitational-wave detectors.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/23/ END:VEVENT BEGIN:VEVENT SUMMARY:Nicolas Sanchis-Gual (CENTRA) DTSTART:20210128T130000Z DTEND:20210128T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/24 DESCRIPTION:Title: Light in the dark: GW190521 as a Proca st ar merger\nby Nicolas Sanchis-Gual (CENTRA) as part of Gravity @ SISSA \n\n\nAbstract\nThe detections of gravitational waves are opening a new wi ndow to the\nUniverse. The nature of black holes and neutron stars may now be\nunveiled\, but gravitational radiation may also lead to exciting\ndis coveries of new exotic compact objects\, oblivious to electromagnetic\nwav es. In particular\, Advanced LIGO-Virgo recently reported a short\ngravita tional-wave signal (GW190521) interpreted as a quasi-circular\nmerger of b lack holes\, one at least populating the pair-instability\nsupernova gap. We found that GW190521 is also consistent with\nnumerically simulated sign als from head-on collisions of two (equal mass\nand spin) horizonless vect or boson stars (aka Proca stars). This\nprovides the first demonstration o f close degeneracy between these two\ntheoretical models\, for a real grav itational-wave event.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/24/ END:VEVENT BEGIN:VEVENT SUMMARY:Antoine Lehébel (Instituto Superior Tecnico (IST)) DTSTART:20210225T130000Z DTEND:20210225T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/25 DESCRIPTION:Title: Onset of spontaneous scalarization in gen eralized scalar-tensor theories\nby Antoine Lehébel (Instituto Superi or Tecnico (IST)) as part of Gravity @ SISSA\n\n\nAbstract\nSpontaneous sc alarization is a mechanism that endows relativistic stars and black holes with a nontrivial configuration only when their spacetime curvature exceed s some threshold. Beyond this threshold\, they acquire a nontrivial scalar configuration\, which also affects their structure. The onset of scalariz ation is controlled only by terms that contribute to linear perturbation a round solutions of general relativity. I will present the complete set of these terms in generalized scalar-tensor theories\, and determine the rele vant thresholds in terms of the contributing coupling constants and the pr operties of the compact object.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/25/ END:VEVENT BEGIN:VEVENT SUMMARY:William East (Perimeter Institute for Theoretical Physics) DTSTART:20210219T130000Z DTEND:20210219T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/26 DESCRIPTION:Title: Evolving Binary Black Hole Spacetimes Bey ond Einstein\nby William East (Perimeter Institute for Theoretical Phy sics) as part of Gravity @ SISSA\n\n\nAbstract\nGravitational wave observa tions of black hole and other compact object mergers have given us an unpa ralleled way to test our understanding of gravity\, and have already been used to constrain a number of possible deviations from general relativity. However\, despite the success of these observations\, for many alternativ e theories\, it is unclear how to\, or even if one can\, obtain a full the oretical prediction of what happens\, e.g.\, when two black holes merge. I will discuss recent progress in this regard\, showing how full\, non-pert urbative evolutions of Horndeski theories of gravity can be carried out us ing a modified harmonic formulation. Focusing on the particular case of Ei nstein-scalar-Gauss-Bonnet gravity as a first application\, I will present new results on the dynamics of black hole scalarization and the mergers o f compact objects. These methods can be used to make gravitational wave pr edictions in the strong-field regime\, and to benchmark approximate treatm ents of deviations from general relativity.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/26/ END:VEVENT BEGIN:VEVENT SUMMARY:Shahin Sheikh Jabbari (Institute for Research in Fundamental Scien ces (IPM)) DTSTART:20210204T090000Z DTEND:20210204T100000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/27 DESCRIPTION:Title: Temperature of Black Holes in Horndeski G ravity Theories\nby Shahin Sheikh Jabbari (Institute for Research in F undamental Sciences (IPM)) as part of Gravity @ SISSA\n\n\nAbstract\nHornd eski theories are the most general family of scalar-tensor gravity with se cond order equations of motion. In these theories speeds of propagation o f gravitons and photons are in general different and gravitons move on an effective metric different than the one seen by photons. These theories a dmit black hole solutions with the peculiar feature that they do not satis fy the first law with the entropy given by the Wald formula. We argue that the issue with the first law stems from the fact that black hole temperat ure is not given by the surface gravity of the black hole metric\, but wit h the surface gravity of the effective metric seen by gravitons. The modif ied temperature\, with the entropy unambiguously computed by the solution phase space method\, yields the correct first law. We discuss far-reaching implications of our results for black hole thermodynamics beyond the Horn deski theories\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/27/ END:VEVENT BEGIN:VEVENT SUMMARY:Anna A. Tokareva (University of Jyväskylä\, Finland) DTSTART:20210318T130000Z DTEND:20210318T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/28 DESCRIPTION:Title: Nonlocal self-healing of Higgs inflation< /a>\nby Anna A. Tokareva (University of Jyväskylä\, Finland) as part of Gravity @ SISSA\n\n\nAbstract\nHiggs inflation is known to be a minimal ex tension of the Standard model allowing for the description of the early Un iverse inflation. This model is considered as an effective field theory si nce it has a relatively low cutoff scale\, thus requiring further extensio ns to be a valid description of the reheating phase. We present a novel ap proach to the problem of unitarization and UV completion of the Higgs infl ation model without introducing new massive degrees of freedom. This appro ach is based on an analytic infinite derivative modification of the Higgs field kinetic term. We construct a unitary non-local UV completion of the original Higgs inflation model such that the inflationary stage stays stab le with respect to quantum corrections.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/28/ END:VEVENT BEGIN:VEVENT SUMMARY:Steven Liebling (Long Island University) DTSTART:20210304T130000Z DTEND:20210304T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/29 DESCRIPTION:Title: Neutron Stars Colliding with Compact Obje cts\nby Steven Liebling (Long Island University) as part of Gravity @ SISSA\n\n\nAbstract\nI will discuss a couple of recent projects along with an ongoing one on which I hope to get some feedback. The first recent pro ject studied the effects of a first order\, high density phase transition in the collision of unequal mass neutron star binaries. The second project studied the multimessenger signals arising from the merger of a black hol e--neutron star binary within an effectively force-free magnetosphere. Fin ally\, in on-going work\, we consider a somewhat exotic possibility of a m agnetized primordial black hole colliding with a neutron star.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/29/ END:VEVENT BEGIN:VEVENT SUMMARY:Miguel Zumalacarregui (Max Planck Institute) DTSTART:20210325T150000Z DTEND:20210325T160000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/30 DESCRIPTION:Title: Gravitational Wave lensing beyond Einstei n’s General Relativity\nby Miguel Zumalacarregui (Max Planck Institu te) as part of Gravity @ SISSA\n\n\nAbstract\nGravitational lensing of lig ht is a well established test of gravity. However\, little is known about how gravitational waves (GW) propagate beyond the simplest space-times in theories beyond Einstein’s General Relativity (GR). I will present a fra mework for GW lensing beyond GR at leading order in frequency. The modifie d causal structure and kinetic mixing between metric and additional degree s of freedom leads to new phenomena\, providing clear-cut tests that do no t require an electromagnetic counterpart. I will present detailed predicti ons for static\, spherically symmetric lenses in an quartic Horndeski theo ry in which novel GW lensing effects can provide tests far more stringent than the multi-messenger event GW170817. The next terms in the frequency e xpansion will further enrich the phenomenology of GW lensing and enable ne w precision tests of gravity.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/30/ END:VEVENT BEGIN:VEVENT SUMMARY:Felix-Louis Julie (Johns Hopkins University) DTSTART:20210311T153000Z DTEND:20210311T163000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/31 DESCRIPTION:Title: Gravitational radiation from a binary bla ck hole coalescence in Einstein-scalar-Gauss-Bonnet gravity\nby Felix- Louis Julie (Johns Hopkins University) as part of Gravity @ SISSA\n\n\nAbs tract\nIn this talk I will show how to derive analytic gravitational wavef orms associated to the coalescence of a “hairy” black hole binary in E instein-scalar-Gauss-Bonnet gravity (ESGB). I will present the associated post-Newtonian (PN) Lagrangian and gravitational wave fluxes. The PN frame work relies on reducing the black holes to point particles with scalar-fie ld-dependent masses. In light of the first law of thermodynamics of ESGB b lack holes\, I will show that this procedure amounts to fixing their Wald entropies. As a consequence\, inspiraling ESGB black holes can slowly grow scalar “hair” until they turn into naked singularities. I will then e xtend the scope of the PN approximation to the strong field regime near me rger by generalizing the Effective-One-Body (EOB) formalism to ESGB gravit y.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/31/ END:VEVENT BEGIN:VEVENT SUMMARY:Salvatore Vitale (MIT Kavli Institute) DTSTART:20210409T120000Z DTEND:20210409T130000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/32 DESCRIPTION:Title: Physics and astrophysics with gravitation al waves\nby Salvatore Vitale (MIT Kavli Institute) as part of Gravity @ SISSA\n\n\nAbstract\nFive years after the first direct detection of gra vitational waves\, over 50 compact binary mergers have been discovered in the data of the LIGO and Virgo detectors. The masses and spins of these co mpact objects can be used to tackle multiple problems in physics\, astroph ysics and cosmology. In this talk I will first discuss what can be learned about the properties of the individual gravitational-wave sources\, and h ow the results depend on some of the analysis details\, such as Bayesian p riors and noise treatment. I will then discuss what can be learned from t he overall set of detections. As an example\, I will report on recent cons traints on the existence of ultralight scalar bosons obtained using the la test LIGO/Virgo data release.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/32/ END:VEVENT BEGIN:VEVENT SUMMARY:Sébastien Renaux-Petel (Institut Astrophysique de Paris) DTSTART:20210401T120000Z DTEND:20210401T130000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/33 DESCRIPTION:Title: Probing primordial features with the Stoc hastic Gravitational Wave Background\nby Sébastien Renaux-Petel (Inst itut Astrophysique de Paris) as part of Gravity @ SISSA\n\n\nAbstract\nFea tures of the primordial density fluctuations power spectrum are theoretica lly extremely motivated and detecting them would provide a unique insight into the physics of the early universe. In this talk\, I will show how the stochastic gravitational wave background (SGWB) offers a new way to probe primordial features\, on small scales complementary to the ones probed by the Cosmic Microwave Background and large scale structure observations. T hese features give rise to specific oscillatory patterns in the frequency profile of the SGWB\, which can be detected in future GW observatories lik e LISA.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/33/ END:VEVENT BEGIN:VEVENT SUMMARY:Andreas Mantziris (Imperial College London) DTSTART:20210415T120000Z DTEND:20210415T130000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/34 DESCRIPTION:Title: Cosmological implications of electroweak vacuum instability: constraints on the Higgs curvature coupling from infla tion\nby Andreas Mantziris (Imperial College London) as part of Gravit y @ SISSA\n\n\nAbstract\nThe current experimentally measured parameters of the Standard Model (SM) suggest that our universe lies in a metastable el ectroweak vacuum\, where the Higgs field could decay to a lower vacuum sta te with catastrophic consequences. Our measurements dictate that such an e vent has not happened yet\, despite the many different mechanisms that cou ld have triggered it during our past light-cone. Via this observation\, we can establish a promising link between cosmology and particle physics and thus constrain important parameters of our theories. The focus of our wor k has been to explore this possibility by calculating the probability of t he false vacuum to decay during the period of inflation and using it to co nstrain the last unknown renormalisable SM parameter $\\xi$\, which couple s the Higgs field with space-time curvature. In our latest study\, we deri ved lower bounds for the Higgs-curvature coupling from vacuum stability in three inflationary models: quadratic and quartic chaotic inflation\, and Starobinsky-like power-law inflation. In contrast to most previous studies \, we took the time-dependence of the Hubble rate into account both in the geometry of our past light-cone and in the Higgs effective potential\, wh ich is approximated with three-loop renormalisation group improvement supp lemented with one-loop curvature corrections. We find that in all three mo dels\, the lower bound is $\\xi \\gtrsim 0.051 ... 0.066$ depending on the top quark mass. We also demonstrated that vacuum decay is most likely to happen a few e-foldings before the end of inflation.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/34/ END:VEVENT BEGIN:VEVENT SUMMARY:Dominik Schleicher (University of Concepción) DTSTART:20210527T120000Z DTEND:20210527T130000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/35 DESCRIPTION:Title: Formation of the first supermassive black holes\nby Dominik Schleicher (University of Concepción) as part of G ravity @ SISSA\n\n\nAbstract\nFor the origin of the first supermassive bla ck holes in the Universe\, different scenarios have been proposed\, rangin g from the direct collapse of massive gas clouds into one single object\, run-away collisions in very dense stellar clusters\, as well as accretion of initially stellar-mass black holes. In this talk I will present progres s from the last several years in these different scenarios\, starting with systematic tests of the direct collapse scenario and the conditions under which it is feasible. I will also discuss the possibility to have purely collison-based scenarios and their possible problems. Finally\, I will pre sent a new mixed scenario where the formation of a massive object is due t o the interplay of collisions and accretions\, including new results from recent numerical simulations.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/35/ END:VEVENT BEGIN:VEVENT SUMMARY:Valeriya Korol (University of Birmingham) DTSTART:20210610T120000Z DTEND:20210610T130000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/36 DESCRIPTION:Title: Galactic Astronomy with LISA\nby Vale riya Korol (University of Birmingham) as part of Gravity @ SISSA\n\n\nAbst ract\nWhite dwarf stars are a well-established tool for studying the Milky Way.\nTwo white dwarfs in a tight orbit forming a double white dwarf (DWD )\nbinary offer to us an additional messenger - gravitational waves - for \nexploring the Galaxy and its immediate surroundings. Gravitational waves \nproduced by DWDs can be detected by the future Laser Interferometer Spac e\nAntenna (LISA). I will discuss what we will learn about our Galaxy from \nthe LISA sample of DWDs. In particular\, I will demonstrate how well the \ndensity distribution of DWDs constrains scale parameters of the Milky\nW ay's bulge\, disc and central bar. Finally\, I will show that massive\nGa lactic satellites can be seen in the gravitational wave sky and I will\npr esent which of their properties we will be able to investigate with\nLISA. \n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/36/ END:VEVENT BEGIN:VEVENT SUMMARY:Macarena Lagos (Columbia University) DTSTART:20210512T120000Z DTEND:20210512T130000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/37 DESCRIPTION:Title: Interacting Gravitational Waves\nby M acarena Lagos (Columbia University) as part of Gravity @ SISSA\n\n\nAbstra ct\nGravitational waves (GWs) allow us to probe the content of the Univers e and the behaviour of gravity on cosmological scales\, through informatio n contained in their propagation. For instance\, the presence of dynamical fields interacting non-minimally with gravity may induce a non-trivial pr opagation of GWs\, changing their propagation speed\, dispersion relation\ , or detected amplitude\, among others. In this talk\, I will discuss part icular cosmological scenarios where GWs interact with another tensor field \, such as in the theory of massive bigravity. I will illustrate explicitl y how the GW signal from a coalescence of black holes gets distorted durin g propagation\, generating specific features such as echoes of the GW sign al emitted. These strong features suggest that stringent constraints on in teracting GWs can be placed with current and future GW detectors.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/37/ END:VEVENT BEGIN:VEVENT SUMMARY:Christopher Berry (Northwestern University) DTSTART:20210520T120000Z DTEND:20210520T130000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/38 DESCRIPTION:Title: On the origin of binary black holes\n by Christopher Berry (Northwestern University) as part of Gravity @ SISSA\ n\n\nAbstract\nGravitational-wave astronomy provides a unique insight into the lives of black holes. Since the beginning of the advanced-detector er a in 2015\, we have observed gravitational waves from over 40 binary black hole systems. Using the measured gravitational-wave signals we can infer the properties of their source systems\, and uncover new insights about th eir formation. There are currently many mysteries around how massive stars evolve and binaries form in order to create the population of binary blac k holes. I will explain how we can use the growing catalogue of gravitatio nal-wave observations to unravel these mysteries and review our discoverie s to date.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/38/ END:VEVENT BEGIN:VEVENT SUMMARY:Marija Tomasevic (University of Barcelona) DTSTART:20210603T120000Z DTEND:20210603T130000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/39 DESCRIPTION:Title: Time in traversable wormholes\nby Mar ija Tomasevic (University of Barcelona) as part of Gravity @ SISSA\n\n\nAb stract\nThe last couple of years have greatly illuminated the underlying p hysics of traversable wormholes. We now know how to construct such solutio ns with the help of certain quantum effects\, and a more precise connectio n between wormholes and entanglement is just beginning to emerge. However\ , older work indicates that these solutions must either allow for seemingl y pathological behavior\, namely that of generic time machine creation\, o r resort to unknown quantum gravity effects that would prevent such pathol ogies. Here we will show how simple\, low-energy arguments are enough to m ake time travel (at least) via wormholes impossible.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/39/ END:VEVENT BEGIN:VEVENT SUMMARY:Pedro Cunha (Max Planck Institute) DTSTART:20210624T120000Z DTEND:20210624T130000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/40 DESCRIPTION:Title: Constraining ultralight scalar fields aro und the M87 black hole using the EHT shadow\nby Pedro Cunha (Max Planc k Institute) as part of Gravity @ SISSA\n\n\nAbstract\nHypothetical ultral ight bosonic fields will spontaneously form macroscopic bosonic halos arou nd Kerr black holes\, via superradiance\, transferring part of the mass an d angular momentum of the black hole into the halo. Such a process\, howev er\, is only efficient if resonant: when the Compton wavelength of the fie ld approximately matches the gravitational scale of the black hole. For a complex-valued field\, the process can form a stationary\, bosonic field-b lack hole equilibrium state - a black hole with synchronised hair. For suf ficiently massive black holes\, such as the one at the centre of the M87 s upergiant elliptical galaxy\, the hairy black hole can be robust against i ts own superradiant instabilities\, within a Hubble time. Studying the sha dows of such scalar hairy black holes\, we can constrain the amount of hai r which is compatible with the Event Horizon Telescope (EHT) observations of the M87 supermassive black hole\, assuming the hair is a condensate of ultralight scalar particles of mass ∼1E−20 eV\, as to be dynamically v iable. We show the EHT observations set a weak constraint\, in the sense t hat typical hairy black holes that could develop their hair dynamically\, are compatible with the observations\, when taking into account the EHT er ror bars and the black hole mass/distance uncertainty. We will also discu ss a recent theorem establishing that an equilibrium Black Hole must admit \, under generic conditions\, at least one circular Light Ring orbit outsi de the horizon. The proof relies on a topological argument and makes virtu ally no assumptions on the matter content or gravity model.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/40/ END:VEVENT BEGIN:VEVENT SUMMARY:Maximilliano Isi (MIT Kavli Institute) DTSTART:20210618T120000Z DTEND:20210618T130000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/41 DESCRIPTION:Title: Testing general relativity with LIGO and Virgo\nby Maximilliano Isi (MIT Kavli Institute) as part of Gravity @ SISSA\n\n\nAbstract\nThe LIGO and Virgo gravitational wave detectors carri ed out the first half of their third observing run from April through Octo ber\, 2019. During this period\, they collected 39 new detections of compa ct binary coalescences\, compiled in the second LIGO-Virgo catalog (GWTC-2 ). These and previous signals contain invaluable information about the nat ure of gravity\, which can be used to learn about black holes and test gen eral relativity. In this talk\, I will provide an overview of these effort s\, with a special focus on probes of black hole ringdowns. I will first s ummarize and contextualize recent results\, and then close by outlining so me of the open questions and challenges that make this a vibrant field of research.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/41/ END:VEVENT BEGIN:VEVENT SUMMARY:Stephen Green (Max Planck Institute for Gravitational Physics) DTSTART:20210506T110000Z DTEND:20210506T120000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/43 DESCRIPTION:Title: Simulation-based inference for compact bi naries\nby Stephen Green (Max Planck Institute for Gravitational Physi cs) as part of Gravity @ SISSA\n\n\nAbstract\nOver the past five years\, L IGO and Virgo have published 50 detections of gravitational waves from com pact binary coalescences. To determine the properties of the astrophysical sources\, Bayes’ theorem is typically combined with an iterative sampli ng algorithm such as MCMC to draw samples from the posterior—by repeated ly generating waveforms and comparing to measured strain data—a process that takes from hours to weeks for a single event. In this talk\, I will d escribe a radically different approach\, using simulation-based inference with deep neural networks to learn a non-iterative surrogate model for the posterior. After training on simulated data\, I will show that these netw orks can accurately analyze real binary black holes in seconds\, with resu lts nearly indistinguishable from standard algorithms. This approach there fore represents a path to faster multimessenger alerts and a means to addr ess the growing rate of detections. I will conclude by discussing prospect s for moving beyond standard algorithms not just in terms of speed\, but i n accuracy as well.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/43/ END:VEVENT BEGIN:VEVENT SUMMARY:Christian Krüger (University of Tübingen) DTSTART:20211026T130000Z DTEND:20211026T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/44 DESCRIPTION:Title: Fast Rotating Neutron Stars: Spectra and Stability without Approximation\nby Christian Krüger (University of T übingen) as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/44/ END:VEVENT BEGIN:VEVENT SUMMARY:Matteo Bonetti (University of Milan Bicocca) DTSTART:20211109T140000Z DTEND:20211109T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/45 DESCRIPTION:Title: The massive black hole binary path to coa lescence\nby Matteo Bonetti (University of Milan Bicocca) as part of G ravity @ SISSA\n\n\nAbstract\nMassive black hole binaries (MBHBs) are expe cted to form at the centre of merging galaxies during the hierarchical ass embly of the cosmic structure and are expected to be the loudest sources o f gravitational waves (GWs) in the low frequency domain surveyed by the on going Pulsar Timing Array (PTA) campaigns and by the forthcoming LISA obse rvatory.\nA meaningful assessment of the detection prospects of the above experiments critically depends on the abundance and properties of MBHBs th at form and evolve during the cosmic history. Therefore\, understanding th e MBH dynamical evolution before and after these binaries form is of param ount importance.\nIn this talk I will review the current understanding of MBHB evolution by analysing the several dynamical processes driving MBHBs at different scales and highlighting possible evolutionary bottlenecks tha t may arise along their path to coalescence.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/45/ END:VEVENT BEGIN:VEVENT SUMMARY:Alexander Vikman (CEICO) DTSTART:20211130T140000Z DTEND:20211130T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/46 DESCRIPTION:Title: Frozen Axions and Global Dynamics for New ton and Planck\nby Alexander Vikman (CEICO) as part of Gravity @ SISSA \n\n\nAbstract\nI will discuss scale-free Einstein equations\, recently in troduced in e-Print: 2011.07055\, where the information from their trace p art is lost. These equations are classically equivalent to General Relativ ity\, yet the Newton constant becomes a constant of integration or a globa l dynamical degree of freedom. Thus\, from the point of view of standard q uantization\, this effective Newton constant is susceptible to quantum flu ctuations. This is similar to what happens to the cosmological constant in unimodular gravity where the trace part of the Einstein equations is lost in a different way. Using analogy with the Henneaux-Teitelboim covariant action for unimodular gravity\, we consider different general-covariant ac tions resulting in these dynamics. This setup allows one to formulate the Heisenberg uncertainty relations for the Newton constant and canonically c onjugated quantities. Interestingly\, a quasiclassical description in thes e global theories requires a minimal level of quantum fluctuations of the Newton constant in the same way as cosmological constant has a minimal lev el of quantum fluctuations in the unimodular gravity\, see e-Print: 2107.0 9601. Unexpectedly\, one of such theories also promotes Planck's quantum c onstant to a global degree of freedom\, which is subject to quantum fluctu ations. \nFollowing analogy with the unimodular gravity\, we discuss non-c ovariant "unimatter" and "unicurvature" gravities describing the scale-fre e Einstein equations. Finally\, we show that in some limit of the Yang-Mil ls gauge theory a "frozen" axion-like field can emulate not only the cosmo logical constant\, but also the gravitational Newton constant or even of t he quantum Planck constant.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/46/ END:VEVENT BEGIN:VEVENT SUMMARY:Alexander Vikman (CEICO) DTSTART:20211202T090000Z DTEND:20211202T100000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/47 DESCRIPTION:Title: Dark Matter via Inverse Phase Transition: going beyond freeze-in with observable Gravitational Waves\nby Alexan der Vikman (CEICO) as part of Gravity @ SISSA\n\n\nAbstract\nI will discus s a recently proposed class of models where Dark Matter (DM) is produced v ia an inverse phase transition. The inverse phase transition can be caused by coupling to some cosmological field. For instance\, this field can be the Ricci scalar\, as in e-Print: 2004.03410\; primordial magnetic field\, as in e-Print: 2010.03383\; or thermal fluctuations of other fields\, as in e-Print: 2104.13722. In this most recent work DM is modelled as a real scalar\, which interacts with the hot primordial plasma through a portal c oupling to another scalar field. For a particular sign of the coupling\, t his system exhibits an inverse phase transition. The latter leads to an ab undant DM production\, even if the portal interaction is so weak that the freeze-in mechanism is inefficient. The model predicts domain wall formati on in the early Universe\, long before the inverse phase transition. These domain walls have a tension decreasing with time\, and completely disappe ar at the inverse phase transition\, so that the problem of overclosing th e Universe is avoided. The domain wall network emits gravitational waves w ith characteristics defined by those of DM. In particular\, the peak frequ ency of gravitational waves (GW) is determined by the portal coupling cons tant. For some range of parameters of the model these GW fall in the obser vable range for currently planned gravitational wave detectors.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/47/ END:VEVENT BEGIN:VEVENT SUMMARY:Laura Bernard (Laboratoire Univers et Théories (LUTH)) DTSTART:20220111T140000Z DTEND:20220111T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/48 DESCRIPTION:Title: Some aspects of gravitational wave modell ing in general relativity and scalar-tensor theories\nby Laura Bernard (Laboratoire Univers et Théories (LUTH)) as part of Gravity @ SISSA\n\n\ nAbstract\nSince the first gravitational wave (GW) detection by the LIGO-V irgo collaboration\, we have now detected more than fifty GW signals from compact binary systems (made of black hole or neutron stars). In the futur e\, the LISA space-based interferometer and the next generation detectors\ , such as the Einstein Telescope\, will allow to test our gravitational pa radigm with an unprecedented precision. One of the new challenge to analys is the forthcoming huge amount of data resides in the high precision model ling of GWs both in general relativity (GR) and beyond. In this talk\, I w ill focus on the post-Newtonian method that is used to describe the inspir al phase of the coalescence of compact binary systems. After reviewing the multipolar - post Minkowskian - post Newtonian formalism and the state-of -the-art in GR\, I will explain how such a formalism can be simply applied to scalar- tensor theories of gravity. In particular\, I will focus on th e main phenomenological differences from GR and present the latest develop ments\, including the contribution from the scalar dipolar tidal effect.\ n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/48/ END:VEVENT BEGIN:VEVENT SUMMARY:Adrien Kuntz (Scuola Normale Superiore) DTSTART:20220929T130000Z DTEND:20220929T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/49 DESCRIPTION:Title: Three-body problem in General Relativity< /a>\nby Adrien Kuntz (Scuola Normale Superiore) as part of Gravity @ SISSA \n\nLecture held in 132.\n\nAbstract\nThree-body systems are very common i n the universe and it is likely that future gravitational-wave detectors w ill detect them and measure their parameters. I will introduce a new appro ach ("Effective Two-Body") perturbatively solving the motion of hierarchic al three-body systems by relying on the existence of two expansion paramet ers: small velocities and large separation of the third body. I will show how this new EFT formulation allows to compute the relativistic Hamiltonia n of three-body systems order-by-order\, and I will present some applicati ons to long-term evolution of three-body systems and waveform modelling.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/49/ END:VEVENT BEGIN:VEVENT SUMMARY:Joao Rosa (Tartu University) DTSTART:20221005T130000Z DTEND:20221005T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/50 DESCRIPTION:Title: Observational signatures of isotropically emitting sources orbiting bosonic stars\nby Joao Rosa (Tartu Universi ty) as part of Gravity @ SISSA\n\nLecture held in 138.\n\nAbstract\nPushed by a number of advances\, electromagnetic observatories have now reached the horizon scale of supermassive black holes. The existence and propertie s of horizons in our universe is one of the outstanding fundamental issues that can now be addressed. Here we investigate the ability to discriminat e between black holes and compact\, horizonless objects\, focusing on the lensing of hot spots and accretion disks around compact objects. We work i n particular with boson and Proca stars as central objects\, and show that the absence of a horizon gives rise to a characteristic feature -- photon s that plough through the central object and produce an extra image. This feature should be universal for central objects made of matter weakly coup led to the standard model.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/50/ END:VEVENT BEGIN:VEVENT SUMMARY:Boris Goncharov (Gran Sasso Science Institute (GSSI)) DTSTART:20221012T130000Z DTEND:20221012T140000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/51 DESCRIPTION:Title: A recipe for detecting the gravitational- wave background with pulsar timing arrays\nby Boris Goncharov (Gran Sa sso Science Institute (GSSI)) as part of Gravity @ SISSA\n\nLecture held i n 138.\n\nAbstract\nWhen galaxies merge\, supermassive black holes at thei r centres form binaries. The binaries that are brought together to separat ions below ~ 0.1 parsec are expected to experience an adiabatic inspiral d ominated by gravitational wave emission. The detection of these signals is a primary goal of pulsar timing arrays (PTA). These experiments observe m illisecond pulsars that act as very precise clocks scattered around our ga laxy. It is expected that the stochastic superposition of supermassive bla ck hole binaries will form a background signal that will be detected prior to individually-resolved sources. Interestingly\, PTAs might now be seein g a spatially-uncorrelated component of the gravitational-wave background. This is to be confirmed or ruled out in the near future based on a better handle on spatial correlations of the signal. In this talk\, I will outli ne the main ingredients necessary to detect the gravitational-wave backgro und\, the flavors it may have\, and the new science it may bring to the ta ble.\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/51/ END:VEVENT BEGIN:VEVENT SUMMARY:Stefano Rinaldi (University of Pisa) DTSTART:20221116T140000Z DTEND:20221116T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/52 DESCRIPTION:by Stefano Rinaldi (University of Pisa) as part of Gravity @ S ISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/52/ END:VEVENT BEGIN:VEVENT SUMMARY:Mario Herrero-Valea (Juan de la Cierva) DTSTART:20221123T140000Z DTEND:20221123T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/53 DESCRIPTION:by Mario Herrero-Valea (Juan de la Cierva) as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/53/ END:VEVENT BEGIN:VEVENT SUMMARY:Enrico Barausse DTSTART:20240111T140000Z DTEND:20240111T160000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/54 DESCRIPTION:Title: Gravitational Waves / Room 135\nby En rico Barausse as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/54/ END:VEVENT BEGIN:VEVENT SUMMARY:Ramit Dey DTSTART:20240118T133000Z DTEND:20240118T143000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/62 DESCRIPTION:Title: Online APP Seminar Host: Stefano Liberati \nby Ramit Dey as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/62/ END:VEVENT BEGIN:VEVENT SUMMARY:Tim Linden DTSTART:20240208T133000Z DTEND:20240208T143000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/94 DESCRIPTION:Title: APP Seminar\nby Tim Linden as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/94/ END:VEVENT BEGIN:VEVENT SUMMARY:Arianna Renzini DTSTART:20240118T090000Z DTEND:20240118T100000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/95 DESCRIPTION:Title: Room 128: Searching for Gravitational-wav e Backgrounds: targets\, methods\, and broad implications\nby Arianna Renzini as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/95/ END:VEVENT BEGIN:VEVENT SUMMARY:Stefano Ascenzi DTSTART:20240119T090000Z DTEND:20240119T100000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/96 DESCRIPTION:Title: Room 128: Gamma-ray bursts and neutron st ars in the multimessenger era\nby Stefano Ascenzi as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/96/ END:VEVENT BEGIN:VEVENT SUMMARY:Silvia Celli DTSTART:20240123T090000Z DTEND:20240123T100000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/97 DESCRIPTION:Title: Room 128: Supernova remnants and star clu sters as candidate cosmic-ray accelerators\nby Silvia Celli as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/97/ END:VEVENT BEGIN:VEVENT SUMMARY:Jieshuang Wang DTSTART:20240125T140000Z DTEND:20240125T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/98 DESCRIPTION:Title: Room 128: Multi-messenger astrophysics: n eutron star mergers and active galactic nucleus jet\nby Jieshuang Wang as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/98/ END:VEVENT BEGIN:VEVENT SUMMARY:Alessia Franchini DTSTART:20240215T090000Z DTEND:20240215T100000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/99 DESCRIPTION:Title: APP Seminar/ Room 128: Electromagnetic em ission from gravitational waves sources\nby Alessia Franchini as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/99/ END:VEVENT BEGIN:VEVENT SUMMARY:Chantal Laure Pitte (SISSA) DTSTART:20241205T133000Z DTEND:20241205T150000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/100 DESCRIPTION:Title: LISA and the No-Hair Theorem: Efforts To wards Precision Tests\nby Chantal Laure Pitte (SISSA) as part of Gravi ty @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/100/ END:VEVENT BEGIN:VEVENT SUMMARY:Marina De Amicis (Niels Bohr Institute) DTSTART:20241216T133000Z DTEND:20241216T143000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/101 DESCRIPTION:Title: A fairy-TAIL story\nby Marina De Ami cis (Niels Bohr Institute) as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/101/ END:VEVENT BEGIN:VEVENT SUMMARY:Ricardo Della Monica (Universidad de Salamanca) DTSTART:20241219T133000Z DTEND:20241219T143000Z DTSTAMP:20260404T095134Z UID:GeneralRelativityandModifiedGrav/102 DESCRIPTION:Title: -\nby Ricardo Della Monica (Universi dad de Salamanca) as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/GeneralRelativityandModi fiedGrav/102/ END:VEVENT END:VCALENDAR