BEGIN:VCALENDAR VERSION:2.0 PRODID:researchseminars.org CALSCALE:GREGORIAN X-WR-CALNAME:researchseminars.org BEGIN:VEVENT SUMMARY:Alberto Salvio (U. Rome and INFN) DTSTART:20200521T133000Z DTEND:20200521T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/1 DESCRIPTION:Title: Inflation and Ultracompact Objects in Quadratic Gravity\nby Albe rto Salvio (U. Rome and INFN) as part of CENTRA Seminar\n\n\nAbstract\nAn extension of general relativity obtained by adding quadratic terms to the action will be considered. Such theory is a UV completion of GR: the addit ional terms soften gravity above a certain scale and render gravity renorm alizable. The presence of 4 derivatives implies via the Ostrogradsky theor em that the classical Hamiltonian is unbounded from below. Nevertheless\, I will argue that the relevant solutions are not unstable\, but metastable : when the energies are much below a threshold (that is high enough to des cribe the whole cosmology) runaways are avoided. Remarkably\, the chaotic inflation theory of initial conditions ensures that such bound is satisfie d and testable implications for the early universe will be discussed. I wi ll also argue that the basic unitarity condition is satisfied. Moreover\, thanks to the UV softening of gravity in this theory\, sufficiently light objects must be horizonless and explicit analytic examples of horizonless ultracompact objects (UCOs) will be discussed. These UCOs are more compact than Schwarzschild black holes and their spacetime is regular everywhere. Due to the lack of a horizon\, light UCOs do not evaporate and\, therefor e\, they may play the role of dark matter.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Hans Bantilan (Queen Mary\, U. of London) DTSTART:20200528T133000Z DTEND:20200528T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/2 DESCRIPTION:Title: Real-time Dynamics of Plasma Balls\nby Hans Bantilan (Queen Mary \, U. of London) as part of CENTRA Seminar\n\n\nAbstract\nIn this talk\, I will describe the first simulations of finite-sized black holes that are dual to droplets of deconfined plasma surrounded by a confining vacuum kno wn as plasma balls. These solutions are obtained by solving the Einstein f ield equations with a negative cosmological constant in four spatial dimen sions\, where one of the spatial coordinates is compactified to form a cir cle whose size shrinks to zero size at the IR bottom of the geometry. The dual gauge theory is four-dimensional\, $\\mathcal{N}=4$ super Yang-Mills compactified on a circle with supersymmetry-breaking boundary conditions. I will show simulations where prompt scalar field collapse produces an exc ited black hole at the IR bottom together with gravitational and scalar ra diation\, in a process that corresponds to particle production in the dual gauge theory.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Bruno Ribeiro (Leiden Observatory\, Leiden U.) DTSTART:20200604T133000Z DTEND:20200604T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/3 DESCRIPTION:Title: The evolving shapes of star-forming galaxies in the young Universe\nby Bruno Ribeiro (Leiden Observatory\, Leiden U.) as part of CENTRA Se minar\n\n\nAbstract\nThe global properties of galaxies show a strong evolu tion of the star formation rate and stellar mass density at the epoch of g alaxy assembly\, driven by several competing physical processes (merging\, accretion\, feedback\, environment\,...). The morphological properties of galaxies are also strongly evolving over the same timescales. In such ear ly stage evolution\, galaxy evolution is believed to be a turbulent proces s where gas inflows\, strong winds and galaxy-galaxy interactions give ris e to the intricate shapes that we encounter in HST photometric observation s of high redshift galaxies. The shape of galaxies is a simple\, yet funda mental\, property of galaxies. In this talk\, I would like to highlight tw o main results on the evolution of rest-frame UV galaxy morphology at 2Early-type galaxies: climbing to the top of the mass ladder\nby Eric Emsellem (ESO) as part of CENTRA Seminar\n\n\nAbstract\nNearby galaxi es display a range of morphologies\, sizes\, masses\, which are the result s of a complex set of formation and evolution processes. In this talk\, I will focus on early-type galaxies which contain about half of all the star s in our local Universe. I will review our current knowledge of how they f orm\, what are the most important mechanisms which shaped them\, and illus trate how our understanding of these objects changed over the last decade via the use of simulations and integral-field spectroscopy. I will then fo cus on the most massive galaxies\, and report on results from numerical si mulations and an observational campaign conducted with the MUSE spectrogra ph\, which led to some interesting surprises.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Sumanta Chakraborty (IACS\, Kolkata) DTSTART:20200625T133000Z DTEND:20200625T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/5 DESCRIPTION:Title: Searching for theories beyond General Relativity through various obs ervational avenues\nby Sumanta Chakraborty (IACS\, Kolkata) as part of CENTRA Seminar\n\n\nAbstract\nIn this talk I will discuss about various o bservational avenues that have been available recently and can be used to test the structure of gravitational theories at large curvature regime. Th is will include gravitational wave observations\, black hole echo as well as measurement of black hole shadow from the supermassive black hole M87*. Implications will also be discussed.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Lorenzo Annulli (CENTRA\, Instituto Superior Tecnico) DTSTART:20200709T133000Z DTEND:20200709T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/6 DESCRIPTION:Title: Stirred and shaken: dynamical behavior of boson stars and dark matte r cores\nby Lorenzo Annulli (CENTRA\, Instituto Superior Tecnico) as p art of CENTRA Seminar\n\n\nAbstract\nThe nature and properties of dark mat ter are arguably among the most important open issues in science. Interest ing candidates for dark matter include light bosonic \nfields. Such scalar fields can give rise to confined structures\, as boson stars or Q-balls. Boson stars are interesting hypothetical new "dark matter stars"\, but als o good descriptions of dark matter haloes when the fields are ultralight. In this talk\, I'm going to focus on the the dynamical response of Newtoni an bosonic structures when excited by external matter (stars\, planets or black holes) in their vicinities. The study of the dynamics of such bodies is important for a number of reasons\, ranging from stability to the way they interact with surrounding objects (stars\, planets 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 presence of a massive black hole or a star\, the drag exerted by the bosonic clump on stars moving wi thin it\, the flux of energy and momentum induced by coalescing binaries\, etc. I will provide a complete picture of the interaction between black h oles or stars and the ultralight dark matter environment they live in.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Sarp Akcay (University Coll.\, Dublin) DTSTART:20200716T133000Z DTEND:20200716T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/8 DESCRIPTION:Title: Precession in Stellar-mass Compact Binary Inspirals\nby Sarp Akc ay (University Coll.\, Dublin) as part of CENTRA Seminar\n\n\nAbstract\nI first discuss how precessing waveform approximants are generated for LIGO- Virgo parameter estimation. I then introduce a new such approximant called TEOBResumSP that my collaborators and I have been developing. TEOBResumSP is an efficient hybrid scheme for generating precessing gravitational wav eforms that combines post-Newtonian precession equations with effective-on e-body aligned-spin dynamics. The approach Euler-rotates aligned-spin TEOB ResumS waveforms from a precessing frame to an inertial frame via Wigner's D matrices. The scheme is compared to current state-of-the-art precessing approximants NRSurd74q and SEOBNRv4PHM in terms of frequency-domain match es of the $\\el=2$ gravitational-wave strain for approximately 1300 compac t binary inspirals with the initial gravitational-wave frequencies between 20 and 50 Hz and the precessing spin parameter $\\chi_p$ ranging up to on e. The matches are better than 0.965 for 85% of the NRSurd74q comparisons and 75% of the SEOBNRv4PHM set. The largest disagreements occur for large mass ratios and for large spin components along the orbital plane quantifi ed in terms of a new parameter\, $\\Sperp$\, that I introduce. The disagre ements stem from Euler-rotating non-precessing waveforms with constant spi ns\, which can be replaced by time-varying z-components of spins. TEOBResu mSP provides a robust alternative precessing approximant to be employed in the parameter estimation of generic-spin compact binaries.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Alejandro Torres-Orjuela (Peking U.\, Beijing and Peking U.\, Beij ing\, KIAA) DTSTART:20200722T100000Z DTEND:20200722T110000Z DTSTAMP:20260404T111138Z UID:CENTRA/9 DESCRIPTION:Title: Phase Shift of Gravitational Waves induced by Aberration\nby Ale jandro Torres-Orjuela (Peking U.\, Beijing and Peking U.\, Beijing\, KIAA) as part of CENTRA Seminar\n\n\nAbstract\nThe velocity of a gravitational wave (GW) source provides crucial information about its formation and evol ution processes. Previous studies considered the Doppler effect on the pha se of GWs as a potential signature of a time-dependent velocity of the sou rce. However\, the Doppler shift only accounts for the time component of t he wave vector\, and in principle motion also affects the spatial componen ts. In my talk I discuss the latter effect\, known as “aberration” for light\, for GWs and how it affects the waveform modelling of an accelerat ing source. I show that the additional aberrational phase shift could be d etectable in two astrophysical scenarios\, namely\, a recoiling binary bla ck hole (BBH) due to GW radiation and a BBH in a triple system. Further\, I discuss how adding the aberrational phase shift in the waveform template s could significantly enhance the detectability of moving sources.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Erik Lentz (Inst. Astrophys. Gottingen) DTSTART:20200723T133000Z DTEND:20200723T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/10 DESCRIPTION:Title: Breaking the Warp Barrier: Hyper-fast Solitons in Einstein-Maxwell- Plasma Theory\nby Erik Lentz (Inst. Astrophys. Gottingen) as part of C ENTRA Seminar\n\n\nAbstract\nSolitons in space--time capable of transporti ng time-like observers at superluminal speeds have long been tied to viola tions of the weak\, strong\, and dominant energy conditions of general rel ativity. The negative-energy sources required for these solitons must be c reated through energy-intensive uncertainty principle processes as no such classical source is known in particle physics. This talk presents an appr oach for overcoming this barrier\, explicitly constructing a class of soli ton solutions that are capable of superluminal motion and sourced by purel y positive energy densities. The solitons are also shown to be capable of being sourced from the stress-energy of a conducting plasma and classical electromagnetic fields. This is the first example of hyper-fast solitons r esulting from known and familiar sources\, reopening the discussion of sup erluminal mechanisms rooted in conventional physics.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/10/ END:VEVENT BEGIN:VEVENT SUMMARY:Taishi Ikeda (CENTRA\, Instituto Superior Tecnico) DTSTART:20200702T133000Z DTEND:20200702T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/11 DESCRIPTION:Title: Massive scalar field around black hole binary and gravitational mol ecules\nby Taishi Ikeda (CENTRA\, Instituto Superior Tecnico) as part of CENTRA Seminar\n\n\nAbstract\nBlack hole binaries are one of the main s ources of gravitational waves. In the age of gravitational wave astronomy\ , we must understand many properties about black hole binaries.\nIn this t alk\, I will talk about new bound states of massive fields around the bina ries. We numerically construct the bound states and discuss the fundamenta l properties. The bound state can be understood as an analogy of quantum m echanics of molecules which is a solvable model.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/11/ END:VEVENT BEGIN:VEVENT SUMMARY:Sante Carloni (U. of Genova) DTSTART:20200903T133000Z DTEND:20200903T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/12 DESCRIPTION:Title: Discrete Relativistic Positioning Systems\nby Sante Carloni (U. of Genova) as part of CENTRA Seminar\n\n\nAbstract\nI will discuss the de sign for a discrete\, immediate\, simple relativistic positioning system ( rPS) which is potentially able of self-positioning (up to isometries) and operating without calibration or ground control assistance. The design is discussed in 1 + 1 spacetimes\, in Minkowski and Schwarzschild solutions\, as well as in 2 + 1 spacetimes in Minkowski. I will sho in particular tha t the system is self-calibrating and robust under perturbations. The rPS c an be adapted as detectors for the gravitational field and we shall briefl y discuss their role in testing different theoretical settings for gravity . In fact\, rPS is a natural candidate for a canonical method to extract o bservables out of a gravitational theory\, and therefore to design experim ents to test gravity.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Tessa Carver (Cardiff U.) DTSTART:20200910T133000Z DTEND:20200910T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/13 DESCRIPTION:Title: Fully-Coherent Gravitational Wave Searches for Binary Neutron Star Mergers and Inferring Astrophysical Signal Probabilities\nby Tessa Car ver (Cardiff U.) as part of CENTRA Seminar\n\n\nAbstract\nBinary Neutron S tar (BNS) Mergers are some of the most violent events in the universe whic h emit a range of astrophysical messengers and are expected to occur frequ ently\, currently detectable via Gamma-Ray Bursts (GRBs) on a weekly basis . These systems are an ideal target for multi-messenger astronomy due the combination of Gravitational Wave (GW) emission and a powerful jet formed upon coalescence\, demonstrated by the observation of a BNS via GW 170817 and GRB 170817A\, then followed up by a range of lower energy electromagne tic observations. Where these jets accelerate hadrons above TeV energies t here should also be an observable astrophysical neutrino flux\, presenting an opportunity for the first GW-neutrino correlations. I will discuss wor k to improve the efficiency of software pipeline searching for modelled GW signals from BNS mergers. In addition we apply methods to infer astrophys ical probabilities for a catalog of triggered event times and for individu al potential GW candidates. These probabilities could be crucial in focusi ng our energy to the most interest candidates for follow up and evaluating the presence of a population of BNS signals.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/13/ END:VEVENT BEGIN:VEVENT SUMMARY:Edgar Gasperin (CENTRA\, IST) DTSTART:20200917T133000Z DTEND:20200917T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/14 DESCRIPTION:Title: Zero rest-mass fields in Minkowski spacetime close to spatial infin ity\nby Edgar Gasperin (CENTRA\, IST) as part of CENTRA Seminar\n\n\nA bstract\nZero rest-mass fields of spin 1 (the electromagnetic field) and s pin 2 propagating on flat space and their corresponding Newman-Penrose (NP ) constants are studied near spatial infinity. The aim of this analysis is to clarify the correspondence between data for these fields on a spacelik e hypersurface and the value of their corresponding NP constants at future and past null infinity. To do so\, the framework of the cylinder at spati al infinity is employed to show that\, expanding the initial data in terms spherical harmonics and powers of the geodesic spatial distance ρ to spa tial infinity\, the NP constants correspond to the data for the second hig hest possible spherical harmonic at fixed order in ρ. In addition\, it is shown that for generic initial data within the class considered in this a rticle\, the NP constants at future and past null infinity\, for both the Maxwell and spin-2 field\, do not correspond to each other. However\, if t he initial data is time-symmetric\, then\, a correspondence between the NP constants at future and past null infinity is established.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/14/ END:VEVENT BEGIN:VEVENT SUMMARY:Marcus Reitz (Radboud U.\, IMAPP) DTSTART:20200924T133000Z DTEND:20200924T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/15 DESCRIPTION:Title: Approximate Killing symmetries in non-perturbative quantum gravity< /a>\nby Marcus Reitz (Radboud U.\, IMAPP) as part of CENTRA Seminar\n\n\nA bstract\nAn open question in quantum gravity is if and how small scale flu ctuations and inhomogeneities behave in such a way that at some larger sca le they can be well approximated by a geometry with some number of exact s ymmetries. Causal Dynamical Triangulation (CDT) is a non-perturbative appr oach to quantum gravity\, based on a lattice regularisation of space-time\ , in which these kind of questions possibly can be addressed. After a shor t introduction of the framework\, I will present a specific notion of appr oximate Killing vectors that can be generalised tosimplicial manifolds usi ng the framework of discrete exterior calculus. These discrete approximate Killing vectors show promise as an observable to study effective symmetri es in quantum gravity. I will present a comparison between three different two-dimensional toy-models of quantum gravity\, CDT\, Dynamical Triangula tions and small perturbations around flat space.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/15/ END:VEVENT BEGIN:VEVENT SUMMARY:María José Bustamante Rosell (Texas U.) DTSTART:20201210T143000Z DTEND:20201210T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/16 DESCRIPTION:Title: Self-torque and frame nutation in binary black hole simulations \nby María José Bustamante Rosell (Texas U.) as part of CENTRA Seminar\n \n\nAbstract\nWe investigate the precession of the spin of the smaller bla ck hole in binary black hole simulations. By considering a sequence of bin aries at higher mass ratios\, we approach the limit of geodetic precession of a test spin. This precession is corrected by the ``self-torque'' due t o the smaller black hole's own spacetime curvature. We find that the spins undergo spin nutations which are not described in conventional descriptio ns of spin precession\, an effect that has been noticed previously in simu lations. These nutations arise because the spins are not measured in a fra me where the smaller hole is stationary. We develop a simple model for the se frame nutations\, extract the instantaneous spin precession rate\, and compare our results to PN and extreme-mass-ratio approximations for the se lf-torque.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/16/ END:VEVENT BEGIN:VEVENT SUMMARY:Alexey Bobrick (Lund Observatory) DTSTART:20201015T133000Z DTEND:20201015T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/17 DESCRIPTION:Title: Binary White Dwarfs and Neutron Stars in the Transient Sky\nby Alexey Bobrick (Lund Observatory) as part of CENTRA Seminar\n\n\nAbstract\ nRecent advances in all-sky synoptic surveys\, their rapid spectroscopic f ollow-up and spectropolarimetry have uncovered a wealth of data about know n transients\, such as type 1a supernovae\, as well as a variety of new cl asses of transient events. In this talk\, I will review the key recent adv ances in our understanding of type 1a supernovae\, both from the observati onal and modelling side. Additionally\, by using white dwarf-neutron star binaries as a show-case\, I will demonstrate how we gradually uncover the nature of new types of transients. Vera Rubin observatory\, coming operati onal in the next two years\, will dramatically advance this already active field of transient research.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/17/ END:VEVENT BEGIN:VEVENT SUMMARY:Hirotada Okawa (Waseda Institute for Advanced Study) DTSTART:20201029T143000Z DTEND:20201029T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/18 DESCRIPTION:Title: Post-Newtonian Kozai-Lidov mechanism and Gravitational waves from h ierarchical triple systems\nby Hirotada Okawa (Waseda Institute for Ad vanced Study) as part of CENTRA Seminar\n\n\nAbstract\nWe have recently st udied gravitational waves from a hierarchical three-body system up to firs t-order postNewtonian approximation. One of the key players is the so-call ed Kozai-Lidov oscillation\, which causes periodic exchange between eccent ricity of inner bindary and relative inclination. In our recent papers\, w e analyzed dynamics of three-body system which consists of pulsars or blac k holes\, and gravitational waves from such systems. In my talk\, I will f irst explain the results obtained so far by perturbation and/or double-ave raging method in the literature and will next discuss our direct simulatio n for three-body problems and those results.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/18/ END:VEVENT BEGIN:VEVENT SUMMARY:Jorge H. C. Martins (Porto U.\, IA) DTSTART:20201001T133000Z DTEND:20201001T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/19 DESCRIPTION:Title: A Nobel Prize for the discovery of other worlds\nby Jorge H. C. Martins (Porto U.\, IA) as part of CENTRA Seminar\n\n\nAbstract\nIn 2019\ , the Nobel Prize of Physics was awarded "for contributions to our underst anding of the evolution of the universe and Earth's place in the cosmos". The prize was actually shared between two subjects that could not be more distinct: cosmology and exoplanetary science. \n\nIn this presentation\, I will speak about the exoplanetary science half of the prize\, the discove ry of an exoplanet orbiting a solar-type star by Michel Mayor and Didier Q ueloz. In particular\, I will focus on how this discovery opened the windo w to a whole new field of astrophysics and drove (and still drives) the de velopment of the new generations of ground based instruments and space mis sions dedicated to the discovery and characterization of the planets aroun d stars other than the Sun.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/19/ END:VEVENT BEGIN:VEVENT SUMMARY:Alejandro Torres-Forne (Potsdam\, Max Planck Inst.) DTSTART:20201022T133000Z DTEND:20201022T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/20 DESCRIPTION:Title: Understanding GWs from core-collapse supernovae\nby Alejandro T orres-Forne (Potsdam\, Max Planck Inst.) as part of CENTRA Seminar\n\n\nAb stract\nCore collapse supernovae is among the most exciting events that we expect to observe in the future by gravitational-wave interferometers. Th ey provide a unique multi-messenger opportunity with the combined emission of gravitational waves\, neutrinos and electromagnetic waves. In this tal k\, I will focus in the current understanding of core-collapse GW signals and how they can be modelled in terms of normal oscillations modes of prot o-neutron stars excited during the post-bounce phase before the onset of t he SN explosion. The observation of such modes in the future by gravitatio nal wave observatories (Virgo\, LIGO) may allow to infer the properties of proto-neutron stars and learn about the engine powering supernova explosi ons.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/20/ END:VEVENT BEGIN:VEVENT SUMMARY:Ippei Obata (Garching\, Max Planck Inst.) DTSTART:20201105T143000Z DTEND:20201105T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/21 DESCRIPTION:Title: Axion Dark Matter Search with Optical Interferometer\nby Ippei Obata (Garching\, Max Planck Inst.) as part of CENTRA Seminar\n\n\nAbstrac t\nAxion dark matter differentiates the phase velocities of the circular-p olarized photons. In this talk\, we present a scheme to measure its phase difference by using a linear optical cavity. We applied this scheme to the Fabry-Perot arm of gravitational wave detectors such as DECIGO\, CE\, and aLIGO. We found that their potential sensitivities to the axion-photon co upling constant\, g_{aγ}\, can reach beyond the current limit of CAST wit h several orders of magnitude\, at a wide axion mass range 10^{-16}eV < m < 10^{-9} eV. Our sensitivity can be achieved without losing any sensitivi ty to gravitational waves. This talk is based on our recent paper Phys. Re v. Lett. 123 (2019) 111301 [arXiv:1903.02017].\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/21/ END:VEVENT BEGIN:VEVENT SUMMARY:Antoine Lehebel (CENTRA\, IST) DTSTART:20201112T143000Z DTEND:20201112T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/22 DESCRIPTION:Title: Onset of spontaneous scalarization in generalized scalar-tensor the ories\nby Antoine Lehebel (CENTRA\, IST) as part of CENTRA Seminar\n\n \nAbstract\nSpontaneous scalarization is a mechanism that endows relativis tic stars and black holes with a nontrivial configuration only when their spacetime curvature exceeds some threshold. Beyond this threshold\, they a cquire a nontrivial scalar configuration\, which also affects their struct ure. The onset of scalarization is controlled only by terms that contribut e to linear perturbation around solutions of general relativity. I will pr esent the complete set of these terms in generalized scalar-tensor theorie s\, and determine the relevant thresholds in terms of the contributing cou pling constants and the properties of the compact object.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/22/ END:VEVENT BEGIN:VEVENT SUMMARY:Juan Diego Soler (Heidelberg\, Max Planck Inst. Astron.) DTSTART:20201119T143000Z DTEND:20201119T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/23 DESCRIPTION:Title: The cycle of matter in the magnetized interstellar medium as reveal ed by machine vision\nby Juan Diego Soler (Heidelberg\, Max Planck Ins t. Astron.) as part of CENTRA Seminar\n\n\nAbstract\nMachine vision (MV) i s the general name given to the methods for automatic inspection and analy sis of images\, from pattern recognition to object classification. I will present the results of MV techniques applied to the study of the formation and evolution of star-forming clouds in the Milky Way\, both in observati ons and numerical simulations. First\, the characterization of filamentary structures in the observations of the atomic hydrogen (HI) emission at 21 cm in The HI/OH/Recombination-line (THOR) survey of the Galactic plane. S econd\, the evaluation of the correlation between the HI emission and the emission from molecular species in star-forming clouds. Finally\, in the s tudy of the anisotropy introduced by the interstellar magnetic fields in t he velocity field in and around star-forming clouds.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/23/ END:VEVENT BEGIN:VEVENT SUMMARY:Clémence Fontanive (Center for Space and Habitability\, Universit y of Bern) DTSTART:20201203T143000Z DTEND:20201203T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/24 DESCRIPTION:Title: Brown dwarfs binaries: from statistics to formation and evolution\nby Clémence Fontanive (Center for Space and Habitability\, University of Bern) as part of CENTRA Seminar\n\n\nAbstract\nThe binary properties o f brown dwarfs in the field form a continuum with the trends observed in t he stellar regime\, with fewer binary systems\, smaller separations and hi gher mass ratios seen around lower-mass objects. However\, the binary stat istics of the latest-type T and Y brown dwarfs are sparse and it is unclea r whether the trends seen for their more massive counterparts hold for the very coolest brown dwarfs. On the other hand\, young brown dwarfs appear to have different multiplicity properties than those observed in the older field population. Measuring and understanding these discrepancies is nece ssary to allow more realistic modelling for formation theories and be able to predict the evolution and fate of binaries. In this talk\, I will pres ent results from a campaign compiled to investigate the binary statistics as a function of age for the extreme low-mass end of the Initial Mass Func tion. Based on constraints from Bayesian statistical analyses\, I will dis cuss the implications of the observed disparities for brown dwarf formatio n and evolution models.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/24/ END:VEVENT BEGIN:VEVENT SUMMARY:Hector O. Silva (Illinois U.\, Urbana) DTSTART:20201126T143000Z DTEND:20201126T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/25 DESCRIPTION:Title: Probing fundamental physics with neutron stars\nby Hector O. Si lva (Illinois U.\, Urbana) as part of CENTRA Seminar\n\n\nAbstract\nNeutro n stars are some of the most extreme objects in Nature. Their large masses (typically around 1.4 times that of the mass) combined with their small r adii (typically around 12 km) result in interior densities that can exceed nuclear saturation density\, above which exotic states of matter can aris e. Moreover\, neutron stars are\, next to black holes\, the strongest gra vitational field sources known. These properties make neutron stars outsta nding laboratories to study both matter and gravity in situations out of r each in terrestrial and Solar System experiments. In this presentation\, I will discuss how recent of neutron star observations\, through both elect romagnetic and gravitational waves\, are allowing us to improve our unders tanding of the internal composition of these stars and to even test Einste in's theory of general relativity.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/25/ END:VEVENT BEGIN:VEVENT SUMMARY:RESCHEDULED DTSTART:20201008T133000Z DTEND:20201008T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/26 DESCRIPTION:by RESCHEDULED as part of CENTRA Seminar\n\nAbstract: TBA\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/26/ END:VEVENT BEGIN:VEVENT SUMMARY:Antonio Mario Magalhães (IAG\, São Paulo U.) DTSTART:20210121T143000Z DTEND:20210121T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/27 DESCRIPTION:Title: Optical Polarimetry and the Galactic Magnetic Field\nby Antonio Mario Magalhães (IAG\, São Paulo U.) as part of CENTRA Seminar\n\n\nAbs tract\nInterstellar optical polarization is produced by dust grains aligne d by a magnetic field and can be used as a tracer of the latter. We discus s the results of our Interstellar Polarization Survey and what we have lea rned about the magnetic field structure of the Galaxy at small and large s cales and at high Galactic latitudes. The data include the Local Interstel lar Medium (ISM) and the nature of the SMC dust and its magnetic field str ucture. We also look into intriguing data concerning the relationship betw een the ambient magnetic field direction and that of disks around young st ars in the Galaxy. \n\nWe describe the numerical tools we are currently de veloping towards a Galactic Magnetic field model. It combines radio (synch rotron) and optical data and a dust model that may explain the observation s. Applications of this model include the interpretation of our optical po larization data towards cosmological fields.\n\nFinally\, we describe our plans for SOUTH POL\, a forthcoming survey of the whole Southern sky in op tical polarized light. SOUTH POL will impact several areas\, from Cosmolog y to Solar System studies.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/27/ END:VEVENT BEGIN:VEVENT SUMMARY:Mikhail Solon (UCLA) DTSTART:20210128T150000Z DTEND:20210128T160000Z DTSTAMP:20260404T111138Z UID:CENTRA/28 DESCRIPTION:Title: Binary Black Holes and Scattering Amplitudes\nby Mikhail Solon (UCLA) as part of CENTRA Seminar\n\n\nAbstract\nFuture gravitational wave detectors will map out and characterize every binary merger in the history of the universe. The possibilities for new and unexpected scientific disc overies from this wealth of data is staggering\, but hinges crucially on c omplementary advances in our theoretical understanding of the nature of gr avitational wave sources. However\, the path from Einstein’s equation to precision binary dynamics is notoriously difficult\, and conventional met hods do not scale to the demands of future detectors. I will describe our recent efforts in solving the relativistic two body problem using modern t ools from quantum field theory.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/28/ END:VEVENT BEGIN:VEVENT SUMMARY:Branislav Nikolic (Cologne U.) DTSTART:20210204T143000Z DTEND:20210204T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/29 DESCRIPTION:Title: Classical\, semiclassical\, and quantum aspects of higher derivativ e gravitational actions\nby Branislav Nikolic (Cologne U.) as part of CENTRA Seminar\n\n\nAbstract\nWhat is the motivation for introducing gravi tational actions containing quadratic curvature or other higher derivative terms in investigations of gravity? What is the classical and quantum int erpretation of such actions and what are the prospects for their observati onal tests?\nIn this talk we address these questions from one approach to quantum gravity: quantum geometrodynamics and its semiclassical limit. We shall draw attention to some conceptual and mathematical inconsistencies t hat quantum geometrodynamics and exact classical quadratic curvature gravi ty suffer from. We emphasize how one must be very cautious with classical and quantum interpretation of higher-derivative actions\, if one wants to maintain a semiclassical limit to quantum geometrodynamics that is consist ent with quantum field theory in curved spacetime. \nWe hope to inspire th e researchers to critically pursue this line of inquiry in other approache s to quantum gravity and their semiclassical limit\, and especially to rev isit the classical interpretation of higher-derivative gravitational actio ns.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/29/ END:VEVENT BEGIN:VEVENT SUMMARY:Patrick Antolin (Northumbria U.) DTSTART:20210211T143000Z DTEND:20210211T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/30 DESCRIPTION:Title: Nanojets of coronal heating\nby Patrick Antolin (Northumbria U. ) as part of CENTRA Seminar\n\n\nAbstract\nThe solar corona is shaped and mysteriously heated to millions of degrees by the Sun’s magnetic field. It has long been hypothesized that the heating results from a myriad of ti ny magnetic energy outbursts called nanoflares\, driven by the fundamental process of magnetic reconnection. Misaligned magnetic field lines can bre ak and reconnect\, producing nanoflares in avalanche-like processes. Howev er\, no direct and unique observations of such nanoflares exist to date\, and the lack of a smoking gun has cast doubt on the possibility of solving the coronal heating problem. From coordinated multi-band high-resolution observations\, we report on the discovery of very fast and bursty nanojets \, the telltale signature of reconnection-based nanoflares resulting in co ronal heating. The nanojet is uniquely characterised by being transverse t o the loop and appears as a unidirectional jet from the reconnection point . Isolated and clustered nanojets are detected\, and a myriad are observed in an avalanche-like progression\, leading to the formation of a coronal loop. Using state-of-the-art numerical simulations\, we demonstrate that t he nanojet is a consequence of the slingshot effect from the magnetically tensed\, curved magnetic field lines reconnecting at small angles. Nanojet s are therefore the key signature of reconnection-based coronal heating in action.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/30/ END:VEVENT BEGIN:VEVENT SUMMARY:Boris Safonov (Sternberg Astronomical Institute\, MSU\, Moscow) DTSTART:20210218T143000Z DTEND:20210218T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/31 DESCRIPTION:Title: Differential Speckle Polarimetry of evolved stars\, including Betel geuse\nby Boris Safonov (Sternberg Astronomical Institute\, MSU\, Mosc ow) as part of CENTRA Seminar\n\n\nAbstract\nDifferential speckle polarime try (DSP) is a method aimed at study of distribution of polarized flux in astrophysical objects at diffraction limited resolution. Using DSP at SAI 2.5 m\, telescope we detected in visual wavelength range dusty envelopes w ith an angular size of 0.05-0.15 arcsec around a number of evolved stars\, e.g. mu Cep (Safonov et al\, MNRAS\, 484\, 5129). Quite frequently these envelopes exhibit variability of morphology associated with the photometri c variability. For example\, in the circumstellar envelope of semiregular variable star V CVn we detected two regions changing their brightness with the same period as the star\, but with significant phase delays\, up to a half of the period. On the basis of these data we suggest that the pulsat ions of V CVn are non-radial (Safonov et al\, AstL\, 45\, 453). In case of Betelgeuse we confirm that the brightness minimum of 2019-2020 is due to the formation of a dust cloud at the line of sight. Apart from this\, duri ng recovery from minimum the amount of scattering dust in the envelope inc reased (arXiv:2005.05215). DSP provides new interesting opportunities to s tudy the mass loss of evolved stars.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/31/ END:VEVENT BEGIN:VEVENT SUMMARY:Yossef Zenati (Johns Hopkins U.) DTSTART:20210311T143000Z DTEND:20210311T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/32 DESCRIPTION:Title: The physical mechanism behind normal and peculiar SN Ia\nby Yos sef Zenati (Johns Hopkins U.) as part of CENTRA Seminar\n\n\nAbstract\nTyp e Ia supernovae (SNe) are thought to originate from the thermonuclear expl osions of carbon-oxygen (CO) white dwarfs (WDs). The proposed progenitors of standard type Ia SNe have been studied for decades and can be\, general ly\, divided into explosions of CO WDs accreting material from stellar non -degenerate companions (single-degenerate\; SD models)\, and those arising from the explosive interaction of two CO WDs (double-degenerate\; DD mode ls). However\, current models for the progenitors of such SNe fail to repr oduce the diverse properties of the observed explosions\, nor do they expl ain the inferred rates and the characteristics of the observed populations of type Ia SNe and their expected progenitors. Here we show that the litt le-studied mergers of CO-WDs with hybrid Helium-CO (He-CO) WDs can provide for a significant fraction of the normal type Ia SNe. Here we use detaile d thermonuclear-hydrodynamical and radiative-transfer models to show that a wide range of mergers of CO WDs with hybrid He-CO WDs can give rise to n ormal type Ia SNe. We find that such He-enriched mergers give rise to expl osions for which the synthetic light-curves and spectra resemble those of observed type Ia SNe\, and in particular\, they can produce a wide range o f peak-luminosities\, MB(MR)~ 18.4 to 19.2 (~ 18.5 to 19:45)\, consistent with those observed for normal type Ia SNe. Moreover\, our population synt hesis models show that\, together with the contribution from mergers of ma ssive double CO-WDs (producing the more luminous SNe)\, they can potential ly reproduce the full range of type Ia SNe\, their rate and delay-time dis tribution.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/32/ END:VEVENT BEGIN:VEVENT SUMMARY:Valerio Faraoni (Bishop’s University\, Sherbrooke\, Canada) DTSTART:20210225T143000Z DTEND:20210225T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/33 DESCRIPTION:Title: Imperfect fluid description of scalar-tensor gravity and an applica tion to the GR limit\nby Valerio Faraoni (Bishop’s University\, Sher brooke\, Canada) as part of CENTRA Seminar\n\n\nAbstract\nScalar-tensor gr avity can be described as general relativity plus an effective imperfect f luid corresponding to the scalar field degree of freedom of this class of theories. A symmetry of electrovacuum Brans-Dicke gravity translates into a symmetry of the corresponding effective fluid. We present the formalism and an application to an anomaly in the limit of Brans-Dicke to Einstein g ravity\, and outline a possible application to the thermodynamics of space time.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/33/ END:VEVENT BEGIN:VEVENT SUMMARY:Poojan Agrawal (Swinburne U.\, Ctr. Astrophys. Supercomput.) DTSTART:20210408T100000Z DTEND:20210408T110000Z DTSTAMP:20260404T111138Z UID:CENTRA/34 DESCRIPTION:Title: Can uncertainties in the evolution of massive stars explain propert ies of gravitational wave progenitors?\nby Poojan Agrawal (Swinburne U .\, Ctr. Astrophys. Supercomput.) as part of CENTRA Seminar\n\n\nAbstract\ nMassive stars play a critical role in the evolution of galaxies and star clusters. Recent observations of the latter have highlighted the need for systematic studies dedicated to probing the impact of massive stellar evol ution on the properties of stellar populations. While the use of fitting f ormulae to stellar tracks remains a popular choice for modelling stellar e volution in population synthesis codes\, these formulae are not adaptable to changes. In this talk\, I will discuss and present results from an alte rnative approach\, one that is more adaptable: Method of Interpolation for Single Star Evolution (METISSE). It can readily make use of stellar model s computed with different stellar evolution codes and compare their predic tions for populations of stars. Using METISSE with the data from different stellar evolution codes\, I will show how various physical ingredients us ed in the evolution of massive stars\, such as the treatment of their radi ation dominated envelopes\, can lead to differences in their evolutionary properties. I will discuss the implications of these differences on the ev olution and interaction of stars in binaries\, and how it can impact compa ct binary mergers and the properties of gravitational wave events.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/34/ END:VEVENT BEGIN:VEVENT SUMMARY:Milton Ruiz (Illinois U.\, Urbana) DTSTART:20210304T143000Z DTEND:20210304T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/35 DESCRIPTION:Title: Full GR simulations of stellar compact binary mergers: from GW17081 7 to GW190814.\nby Milton Ruiz (Illinois U.\, Urbana) as part of CENTR A Seminar\n\n\nAbstract\nStellar Compact object mergers are not only impor tant sources of gravitational waves but also central engines that power el ectromagnetic transients and r-processes\, if matter is involved. I wil l review recent progress modeling the merger of black hole-neutron star an d neutron stars binaries highlighting state-of-the-art general relativisti c magnetohydrodynamic simulations. In particular\, I focus on the effort to establish these systems as viable progenitors of short-hard gamma ray b ursts and understanding their role in triggering the r-process. We use the predictions of these numerical simulations to impose constraints on the n ature of GW170817 and GW190814.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/35/ END:VEVENT BEGIN:VEVENT SUMMARY:Francisco Duque (CENTRA\, Instituto Superior Técnico) DTSTART:20210318T143000Z DTEND:20210318T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/36 DESCRIPTION:Title: Gravitational tuning forks and hierarchical triple systems\nby Francisco Duque (CENTRA\, Instituto Superior Técnico) as part of CENTRA S eminar\n\n\nAbstract\nThe LIGO-Virgo collaboration recently reported evide nce for coalescences involving hierarchical triples composed by a stellar- mass binary system in the vicinity of a supermassive black hole (SMBH). We study gravitational wave emission in the strong-field regime of these sys tems and find that the binary system can resonantly excite the quasinormal modes of the SMBH\, as in the resonant excitation of two tuning forks wit h matching frequencies. Moreover\, the flux of energy crossing the SMBH h orizon can be much more significant than in the standard extreme-mass-rati o inspirals. Consequently\, these systems have a natural mechanism to prob e strong-field physics. This can lead to distinctive signatures in their w aveform such as Doppler shifts\, aberration\, lensing and strong amplitude modulations Finally\, we address the impact of our results for the space- based LISA mission\, which is particularly designed to detect gravitiation al waves originated in galactic centers\, where hierarchical triple system s are known to be abundant.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/36/ END:VEVENT BEGIN:VEVENT SUMMARY:Sabyasachi Goswami (SISSA\, Trieste\, Italy) DTSTART:20210325T143000Z DTEND:20210325T153000Z DTSTAMP:20260404T111138Z UID:CENTRA/37 DESCRIPTION:Title: On the effects of Initial Mass function on the galactic chemical en richment\nby Sabyasachi Goswami (SISSA\, Trieste\, Italy) as part of C ENTRA Seminar\n\n\nAbstract\nContext: There is mounting evidence that the stellar initial mass function (IMF) could extend much beyond the canonical Mi ~100\, Msun limit\, but the impact of such hypothesis on the chemical enrichment of galaxies still remains to be clarified.\n\nAim: We aim to ad dress this question by analysing the observed abundances of thin- and thic k-disc stars in the Milky Way with chemical evolution models that account for the contribution of very massive stars dying as pair-instability super novae.\n\nMethod: We built new sets of chemical yields from massive and ve ry massive stars up to Mi ~ 350 Msun\, by combining the wind ejecta extra cted from our hydrostatic stellar evolution models with explosion ejecta f rom the literature. Using a simple chemical evolution code we analyse the effects of adopting different yield tables by comparing predictions agains t observations of stars in the solar vicinity.\n\nResults: After several t ests\, we focus on the [O/Fe] ratio which best separates the chemical patt erns of the two Milky Way components. We find that with a standard IMF\, t runcated at Mi ~ 100 Msun\, we can reproduce various observational constra ints for thin-disc stars\, but the same IMF fails to account for the [O/ Fe] ratios of thick-disc stars. The best results are obtained by extending the IMF up to Mi = 350 Msun and including the chemical ejecta of very ma ssive stars\, in the form of winds and pair-instability supernova explosio ns.\n\nConclusions: Our study indicates that PISN played a significant rol e in shaping the chemical evolution of the Milky Way thick disc. By includ ing their chemical yields it is easier to reproduce not only the level of the alpha-enhancement but also the observed slope of thick-disc stars in t he [O/Fe] vs [Fe/H] diagram. The bottom line is that the contribution of v ery massive stars to the chemical enrichment of galaxies is potentially qu ite important and should not be neglected in chemical evolution models.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/37/ END:VEVENT BEGIN:VEVENT SUMMARY:Abbas Askar (Lund U.) DTSTART:20210422T133000Z DTEND:20210422T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/38 DESCRIPTION:Title: Black Hole Dynamics in Star Clusters: Evolution and Growth from Ste llar to Supermassive Scales\nby Abbas Askar (Lund U.) as part of CENTR A Seminar\n\n\nAbstract\nOver the past five years\, nearly fifty merging b inary black holes have been discovered through the direct detection of gra vitational waves by the LIGO/Virgo collaboration. While these observations provide unprecedented insights into the demographics of black holes\, the y also raise important questions about the astrophysical origin and format ion of these elusive binary systems. One of the formation channels for the se observed gravitational wave sources are dynamical interactions in dense star cluster. In this talk\, I will describe how star clusters evolve and discuss the various processes by which merging binary black holes can for m in them based on results from state-of-the-art simulations of nearly two thousand stellar clusters. I will also give an overview of the main proce sses involved in the retention and long-term evolution of black holes in s tar clusters and explain how they shape the properties and merger rates fo r binary black holes that originate in these dense stellar environments. A dditionally\, it has also been suggested that massive and dense star clust ers could be potential sites for forming black holes with masses between ~ 100 to 10\,000 solar masses. I will discuss the key processes and caveats involved in the formation\, retention and growth of these intermediate-ma ss black holes in the densest of star clusters. Finally\, I will discuss h ow star clusters that host intermediate-mass black holes can potentially e nd up in the center of the galaxy where they may play a role in seeding th e formation of supermassive black holes.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/38/ END:VEVENT BEGIN:VEVENT SUMMARY:Miren Radia (DAMTP\, Cambridge U.) DTSTART:20210429T133000Z DTEND:20210429T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/39 DESCRIPTION:Title: Anomalies in the gravitational recoil of eccentric black-hole merge rs with unequal mass ratios\nby Miren Radia (DAMTP\, Cambridge U.) as part of CENTRA Seminar\n\n\nAbstract\nThe radiation of linear momentum imp arts a recoil (or "kick") to the center of mass of a merging black hole bi nary system. In 2019\, numerical relativity calculations showed that the a ddition of orbital eccentricity can lead to an approximate 25% increase in recoil velocities for equal-mass\, spinning binaries with spins lying in the orbital plane ("superkick" configurations) [arXiv:1910.01598]. I will present recent results [arXiv:2101.11015] obtained from numerical simulati ons investigating the impact of nonzero eccentricity on the kick magnitude and gravitational-wave emission of nonspinning\, unequal-mass black hole binaries. Like the spinning case\, nonzero eccentricities at merger can le ad to kicks which are larger by up to ~25% relative to the quasicircular c ase. However\, we also find that the kick velocity has an oscillatory depe ndence on the eccentricity. I will discuss our interpretation of this phen omenon and our observations.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/39/ END:VEVENT BEGIN:VEVENT SUMMARY:Fábio Cruz (GoLP\, Instituto Superior Técnico) DTSTART:20210506T133000Z DTEND:20210506T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/40 DESCRIPTION:Title: First-principles kinetic simulations of pulsar magnetospheres\n by Fábio Cruz (GoLP\, Instituto Superior Técnico) as part of CENTRA Semi nar\n\n\nAbstract\nPulsars gather a wealth of extreme physical conditions\ , making them unique environments where general relativity\, quantum elect rodynamics\, and plasma physics meet. The electron-positron plasma that pa rtially fills the pulsar magnetosphere is thought to be created via strong Quantum Electrodynamics (QED) cascades. In each step of this positive fee dback process\, electrons and positrons accelerated to TeV energies emit g amma-rays that\, in the presence of 10^12 Gauss magnetic fields\, decay in to new electron-positron pairs. In this talk\, I will present two classes of fully kinetic particle-in-cell simulations of pulsar magnetospheres. Fi rst\, I will show local simulations including the QED processes relevant i n pulsars from first principles\, and show that plasma waves triggered by QED cascades can produce coherent electromagnetic waves\, that are strong candidates for the longstanding problem of pulsar radio emission. Second\, I will present global simulations\, that demonstrate that QED cascades op erating up to only a few stellar radii above the central neutron star can provide enough plasma to fill the whole pulsar magnetosphere and trigger d issipation at large radii\, consistently with observations. Preliminary re sults of simulations of pulsars where general relativity is taken into acc ount will be presented\, and its role in the global dynamics of the magnet osphere will be discussed.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/40/ END:VEVENT BEGIN:VEVENT SUMMARY:Jonathan Thompson (Cardiff U.) DTSTART:20210415T133000Z DTEND:20210415T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/41 DESCRIPTION:Title: Modelling precession in gravitational waves through inspiral\, merg er and ringdown\nby Jonathan Thompson (Cardiff U.) as part of CENTRA S eminar\n\n\nAbstract\nAs gravitational wave detectors increase in sensitiv ity\, previously unmodelled physical effects will play an important role i n advancing the accuracy of future gravitational wave models. For signals arising from precessing compact binaries\, current models map non-precessi ng waveforms onto the precessing parameter space through a non-inertial ro tation using Euler angles derived from the post-Newtonian dynamics of the inspiraling system. While these angles approximate well the motion of the orbital plane relative to the direction of total (fixed) angular momentum at early times or low frequencies of the signal\, the morphology of these angles disagrees strongly with numerical relativity results through merger and ringdown\, where the post-Newtonian approximation breaks down. We pre sent the first model of these precession angles that has been tuned to pre cessing numerical relativity simulations through merger and ringdown\, and discuss additional changes to the underlying non-precessing waveform need ed to ensure accuracy for more challenging precessing binaries with higher mass ratios and spin magnitudes.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/41/ END:VEVENT BEGIN:VEVENT SUMMARY:Andreas Mantziris (Imperial College) DTSTART:20210513T133000Z DTEND:20210513T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/42 DESCRIPTION:Title: Cosmological implications of electroweak vacuum instability: constr aints on the Higgs curvature coupling from inflation\nby Andreas Mantz iris (Imperial College) as part of CENTRA Seminar\n\n\nAbstract\nSpeaker: Andreas Mantziris (Imperial College)\n\nTitle: Cosmological implications o f electroweak vacuum instability: constraints on the Higgs curvature coupl ing from inflation \n\nAbstract: \nThe current experimentally measured par ameters of the Standard Model (SM) suggest that our universe lies in a met astable electroweak vacuum\, where the Higgs field could decay to a lower vacuum state with catastrophic consequences. Our measurements dictate that such an event has not happened yet\, despite the many different mechanism s that could have triggered it during our past light-cone. Via this observ ation\, we can establish a promising link between cosmology and particle p hysics and thus constrain important parameters of our theories. The focus of our work has been to explore this possibility by calculating the probab ility of the false vacuum to decay during the period of inflation and usin g it to constrain the last unknown renormalisable SM parameter $\\xi$\, wh ich couples the Higgs field with space-time curvature. In our latest study \, we derived lower bounds for the Higgs-curvature coupling from vacuum st ability in three inflationary models: quadratic and quartic chaotic inflat ion\, and Starobinsky-like power-law inflation. In contrast to most previo us studies\, we took the time-dependence of the Hubble rate into account b oth in the geometry of our past light-cone and in the Higgs effective pote ntial\, which is approximated with three-loop renormalisation group improv ement supplemented with one-loop curvature corrections. We find that in al l three models\, the lower bound is $\\xi \\gtrsim 0.051 ... 0.066$ depend ing 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\nRoom: Z OOM videoconference (contact justin.feng@tecnico.ulisboa.pt for URL)\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/42/ END:VEVENT BEGIN:VEVENT SUMMARY:Donato Bini (IAC\, Rome and INFN\, Naples) DTSTART:20210520T133000Z DTEND:20210520T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/43 DESCRIPTION:Title: Recent results in the relativistic two-body problem: the scattering angle\nby Donato Bini (IAC\, Rome and INFN\, Naples) as part of CENTR A Seminar\n\n\nAbstract\nThe recent progress in understanding the features of the relativistic two-body problem has been possible by combining infor mation taken from various different contexts\, namely Post-Newtonian\, P ost-Minkowskian\, Self-Force\, and Effective one-body formalisms. A novel approach (termed "Tutti Frutti") has allowed us to reach the 6PN level of accuracy in the discussion of the problem (modulo some unknown parameter). Other results have already been obtained (and much is currently expected) from Effective Field Theories. The status of the art and the current rese arch trends will be reviewed here.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/43/ END:VEVENT BEGIN:VEVENT SUMMARY:Chen Yuan (ITP\, Chinese Academy of Sciences) DTSTART:20210527T133000Z DTEND:20210527T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/44 DESCRIPTION:Title: Non-tensorial Gravitational Wave Background in NANOGrav 12.5-Year D ata Set\nby Chen Yuan (ITP\, Chinese Academy of Sciences) as part of CENTRA Seminar\n\n\nAbstract\nThe North American Nanohertz Observatory for Gravitational Waves (NANOGrav) collaboration has reported a strong eviden ce of a stochastic process\, modeled as a power-law\, with common amplitud e and spectral index among all pulsars. However\, there is no statisticall y significant evidence for quadrupolar spatial correlations and hence this process can not be explained by a gravitational-wave background (GWB) det ection. We perform a search for an isotropic non-tensorial GWB allowed in general metric theories of gravity in the NANOGrav 12.5-year data set. By modeling the GWB as a power-law spectrum\, we find strong Bayesian evidenc e for a spatially correlated process with scalar transverse (ST) correlati ons.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/44/ END:VEVENT BEGIN:VEVENT SUMMARY:Patrick Bourg (Southampton U.) DTSTART:20210617T133000Z DTEND:20210617T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/45 DESCRIPTION:Title: Critical collapse of a spherically symmetric ultrarelativistic flui d in 2 + 1 dimensions\nby Patrick Bourg (Southampton U.) as part of CE NTRA Seminar\n\n\nAbstract\nWe present new numerical simulations of the gr avitational collapse of a perfect fluid with the ultrarelativistic equatio n of state P = κρ\, in spherical symmetry in 2 + 1 spacetime dimensions with Λ < 0. At the threshold of prompt collapse\, we find type I (lifetim e scales as logarithm of distance from the threshold) and type II critical phenomena (apparent horizon mass and maximum curvature scale as powers of distance from the threshold) depending on κ. Moreover\, the type II crit ical solution is not self-similar (as in higher dimensions) but contractin g quasi-statically.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/45/ END:VEVENT BEGIN:VEVENT SUMMARY:Ali Seraj (Brussels U. and Intl. Solvay Inst.\, Brussels) DTSTART:20210701T133000Z DTEND:20210701T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/46 DESCRIPTION:Title: Gravitational breathing memory and dual symmetries\nby Ali Sera j (Brussels U. and Intl. Solvay Inst.\, Brussels) as part of CENTRA Semina r\n\n\nAbstract\nBrans-Dicke theory contains an additional propagating mod e which causes homogeneous expansion and contraction of test bodies in tra nsverse directions. This "breathing" mode is associated with novel memory effects in addition to those of general relativity. Standard tensor mode m emories are related to a symmetry principle: they are determined by the ba lance equations corresponding to the BMS symmetries. In this paper\, we sh ow that the leading and subleading breathing memory effects are determined by the balance equations associated with the leading and "overleading" as ymptotic symmetries of a dual formulation of the scalar field in terms of a two-form gauge field. The memory effect causes a transition in the vacuu m of the dual gauge theory. These results highlight the significance of du al charges and the physical role of overleading asymptotic symmetries.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/46/ END:VEVENT BEGIN:VEVENT SUMMARY:Rodrigo Panosso Macedo (Queen Mary University of London) DTSTART:20210715T133000Z DTEND:20210715T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/47 DESCRIPTION:Title: Pseudospectrum and black hole quasi-normal mode (in)stability\n by Rodrigo Panosso Macedo (Queen Mary University of London) as part of CEN TRA Seminar\n\n\nAbstract\nWe study the stability of quasi-normal modes (Q NM) in asymptotically flat black hole spacetimes by means of a pseudospect rum analysis. The construction of the Schwarzschild QNM pseudospectrum rev eals: i) the stability of the slowest decaying QNM under perturbations res pecting the asymptotic structure\, reassessing the instability of the fund amental QNM discussed by Nollert (1996)\; ii) the instability of all overt ones under small scale perturbations of sufficiently high frequency\, that migrate to a universal class of QNM branches along pseudospectra boundari es\, shedding light on Nollert & Price's analysis (1996).\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/47/ END:VEVENT BEGIN:VEVENT SUMMARY:Kyriakos Destounis (Tubingen U.) DTSTART:20210608T133000Z DTEND:20210608T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/48 DESCRIPTION:Title: Gravitational-wave imprints of non-integrable extreme-mass-ratio in spirals\nby Kyriakos Destounis (Tubingen U.) as part of CENTRA Seminar \n\n\nAbstract\nThe detection of gravitational waves from extreme-mass-rat io inspirals (EMRIs) with upcoming space-borne detectors will allow for un precedented tests of general relativity in the strong-field regime. Aside from assessing whether black holes are unequivocally described by the Kerr metric\, they may place constraints on the degree of spacetime symmetry. Depending on exactly how a hypothetical departure from the Kerr metric man ifests\, the Carter symmetry\, which implies the integrability of the geod esic equations\, may be broken. In this talk\, I will discuss the impact o f non-integrability in EMRIs which involve a supermassive compact object w ith anomalous multipolar structure. After reviewing the features of chaoti c phenomena in EMRIs\, I will argue that non-integrability is precisely im printed in the gravitational waveform. Explicit examples of non-integrable EMRIs will be discussed\, as well as their role in LISA data analysis.\n\ nThis talk will be based on the following articles:\n\nPhys.Rev.D 102 (202 0) 6\, 064041\nPhys.Rev.Lett. 126 (2021) 14\, 141102\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/48/ END:VEVENT BEGIN:VEVENT SUMMARY:Sjoert van Velzen (Leiden Observ.\, New York U.\, CCPP\, Maryland U.) DTSTART:20210624T133000Z DTEND:20210624T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/49 DESCRIPTION:Title: Stellar tidal disruption events: a new probe for black hole astroph ysics\nby Sjoert van Velzen (Leiden Observ.\, New York U.\, CCPP\, Mar yland U.) as part of CENTRA Seminar\n\n\nAbstract\nThe tidal disruption of a star by a massive black hole is a rare event that results in a spectacu lar flare of electromagnetic radiation. Visible from radio to X-ray wavele ngths\, tidal disruption flares are a unique probe to study massive black holes and the nucleus of their host galaxies. The advent of optical transi ent surveys has accelerated this field\, resulting in a large number of (o ften unexpected) discoveries. I will review this recent progress\, demonst rating the application of tidal disruption events as tools to measure blac k hole spin and the launch mechanism of relativistic jets.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/49/ END:VEVENT BEGIN:VEVENT SUMMARY:David Pereñiguez (Madrid\, IFT) DTSTART:20210708T133000Z DTEND:20210708T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/50 DESCRIPTION:Title: Quasinormal modes of NUT-charged black branes in AdS/CFT\nby Da vid Pereñiguez (Madrid\, IFT) as part of CENTRA Seminar\n\n\nAbstract\nIn the context of AdS/CFT\, the quasinormal modes (QNM) of black holes in th e bulk correspond to the poles of the Green’s functions of the dual fini te-temperature QFT. In this talk I will show how 4d black hole perturbatio n theory in the Newman—Penrose formalism extends to planar black holes i n AdS with NUT charge. Scalar\, electromagnetic and gravitational modes co me organised precisely as Landau levels\, the NUT charge playing the role of a constant magnetic field. I will derive the boundary conditions at inf inity that are relevant for holography\, and conclude by presenting the as sociated QNM spectrum and discussing its main features.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/50/ END:VEVENT BEGIN:VEVENT SUMMARY:Justin Feng (CENTRA\, IST) DTSTART:20210722T133000Z DTEND:20210722T143000Z DTSTAMP:20260404T111138Z UID:CENTRA/51 DESCRIPTION:Title: Self-collision of a portal wormhole\nby Justin Feng (CENTRA\, I ST) as part of CENTRA Seminar\n\n\nAbstract\nPortals (also known as loop b ased thin shell wormholes or gates in the literature) are wormholes suppor ted by a single loop of negative mass\, negative tension cosmic string and have the property that the geometry is everywhere flat except at the cosm ic string. In this talk\, I describe the construction\, topology\, and smo othing of portals\, and consider what happens if one attempts to collide t he mouths of a portal\, which naively resembles a topology changing proces s. For a simple anisotropic fluid\, it is found that in general relativity \, portal mouths do not experience an acceleration as they are brought tog ether\, and a curvature singularity forms in the limit that the separation distance vanishes.\n LOCATION:https://stable.researchseminars.org/talk/CENTRA/51/ END:VEVENT END:VCALENDAR