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:20260422T225700Z UID:GeneralRelativityandModifiedGrav/1 DESCRIPTION:Title: Well-posed formulation of scalar-tensor effective field theory\nby Aron Kovacs (DAMPT\, University of Cambridge) as par t of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/1/ END:VEVENT BEGIN:VEVENT SUMMARY:Jorge Bellorin (Universidad de Antofagasta) DTSTART:20200625T140000Z DTEND:20200625T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/2 DESCRIPTION:Title: Horava gravity in canonical formalism\nby Jor ge Bellorin (Universidad de Antofagasta) as part of Gravity @ SISSA\n\nAbs tract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/2/ END:VEVENT BEGIN:VEVENT SUMMARY:Xisco Jimenez (Max Planck Institute for Gravitational Physics) DTSTART:20200702T130000Z DTEND:20200702T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/3 DESCRIPTION:Title: Ringdown overtones\, black hole spectroscopy\, an d no-hair theorem tests with overtones and angular modes\nby Xisco Jim enez (Max Planck Institute for Gravitational Physics) as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/3/ END:VEVENT BEGIN:VEVENT SUMMARY:Luis Lenher (Perimeter Institute for Theoretical Physics) DTSTART:20200709T140000Z DTEND:20200709T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/4 DESCRIPTION:Title: Extensions to GR: Roadblocks & potential way thro ugh\nby Luis Lenher (Perimeter Institute for Theoretical Physics) as p art of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/4/ END:VEVENT BEGIN:VEVENT SUMMARY:Pantelis Pnigouras (Mathematical Sciences and STAG Research Centre \,University of Southampton\, Southampton\, UK) DTSTART:20200716T140000Z DTEND:20200716T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/5 DESCRIPTION:Title: Secular instabilities in neutron stars\nby Pa ntelis Pnigouras (Mathematical Sciences and STAG Research Centre\,Universi ty of Southampton\, Southampton\, UK) as part of Gravity @ SISSA\n\n\nAbst ract\nAs opposed to dynamical instabilities\, secular instabilities descri be the slow exponential growth of a perturbation\, due to the presence of a dissipation mechanism. We will see how they are related to an old proble m\, regarding the shape of the Earth\, and briefly review their manifestat ion in neutron stars. We will focus on the secular instability driven by t he emission of gravitational waves\, which can be used to derive informati on about the largely unknown neutron star interior composition\, as well a s provide an explanation for some long-standing problems of pulsar observa tions. Finally\, we will present a recently reported study\, according to which this instability affects the evolution of neutron star binaries\, th us becoming potentially relevant for gravitational-wave detections.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/5/ END:VEVENT BEGIN:VEVENT SUMMARY:Alberto Sesana (University of Milan-Bicocca) DTSTART:20200911T140000Z DTEND:20200911T150000Z DTSTAMP:20260422T225700Z 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 waves (G Ws) is shaping our understanding of the Universe. At nHz frequencies\, pul sar timing arrays (PTAs) promise to detect the signal coming from the cosm ological population of supermassive black hole binaries (SMBHBs) within th e next few years. After reviewing the astrophysics of SMBHBs\, I will desc ribe the current status of the PTA effort\, present the most recent limits \, and their astrophysical implications.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/6/ END:VEVENT BEGIN:VEVENT SUMMARY:Katsuki Aoki (Waseda University) DTSTART:20200924T093000Z DTEND:20200924T103000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/7 DESCRIPTION:Title: Gravitational positivity bounds\nby Katsuki A oki (Waseda University) as part of Gravity @ SISSA\n\n\nAbstract\nThe desi red properties of scattering amplitudes such as unitarity yield non-trivia l constraints on low energy effective field theories (EFT)\, called positi vity bounds. The bounds are clearly derived when gravity is ignored while their extensions to include gravity are not straightforward due to a diver gence coming from the graviton t-channel exchange. We study the validity o f positivity bounds in the presence of a massless graviton\, assuming the Regge behavior of the amplitude. Under this assumption\, the problematic t -channel pole is canceled with the UV integral of the imaginary part of th e amplitude in the dispersion relation\, which gives rise to finite correc tions to the positivity bounds. We find that low-energy EFT with "wrong" s ign are generically allowed. The allowed amount of the positivity violatio n is determined by the Regge behavior. This violation is suppressed by $M_ {\\rm pl}^{-2} \\alpha'$ where $\\alpha'$ is the scale of Reggeization. Th is 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. Implications of our results on the degenerate higher-order scalar-tensor (DHOST) theor y are also discussed.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/7/ END:VEVENT BEGIN:VEVENT SUMMARY:Clare Burrage (University of Nottingham) DTSTART:20201001T140000Z DTEND:20201001T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/8 DESCRIPTION:Title: Screening of fifth forces in scalar tensor theori es\nby Clare Burrage (University of Nottingham) as part of Gravity @ S ISSA\n\n\nAbstract\nScalar tensor theories are of interest as possible exp lanations for the acceleration of the expansion of the universe\, and also as a way to understand possible modifications of gravity. However\, it is always necessary to explain why\, if such a theory describes our universe \, a scalar mediated fifth force has not been seen. I will discuss two pos sible explanations for this: (1) that the underlying physical theory is sc ale invariant and (2) that non-linearities in the theory act to suppress\, or 'screen' the fifth force. I will focus\, in particular\, on the chall enges encounter when trying to embed these mechanisms in effective field t heories.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/8/ END:VEVENT BEGIN:VEVENT SUMMARY:Raissa F. P. Mendes (Universidade Federal Fluminense) DTSTART:20201015T140000Z DTEND:20201015T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/9 DESCRIPTION:Title: Neutron stars and screening mechanisms\nby Ra issa F. P. Mendes (Universidade Federal Fluminense) as part of Gravity @ S ISSA\n\n\nAbstract\nScalar-tensor theories of gravity offer an interesting framework for cosmology\, since the new scalar degree of freedom\, when a ctive at the largest scales in the Universe\, could help to drive its acce lerated expansion. At the same time\, the scalar field must conceal its ef fects in solar system scales\, where observations conform extremely well t o general relativity. Such screening of the scalar fifth force is often de nsity-dependent\, and models are usually tuned to general relativity for s olar system densities and higher. In this seminar we explore the possibili ty that screening may actually fail when densities are the highest\, namel y\, in the core of the most compact neutron stars found in nature. We disc uss the necessary microphysical requirements for the nuclear equation of s tate\, as well as some properties of neutron stars with unscreened cores i n a few interesting models.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/9/ END:VEVENT BEGIN:VEVENT SUMMARY:Daniele Viganò (Institute of Space Science CSIC) DTSTART:20201008T140000Z DTEND:20201008T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/10 DESCRIPTION:Title: Turbulent dynamos in binary neutron star mergers \nby Daniele Viganò (Institute of Space Science CSIC) as part of Grav ity @ SISSA\n\n\nAbstract\nOne of the most important open issue in the the oretical understanding of binary neutron star mergers is the amplification of magnetic fields. This happens first in a turbulent way at small scales via Kelvin-Helmholtz instability\, and with a large-scale ordering via wi nding and magneto-rotational instability after. However\, the numerical re solution currently doable with the most expensive simulations (tens of mil lions of CPU hours) is very far from capturing the scales at play (possibl y\, fractions of meters). Here we present how a sub-grid-scale modeling 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 fi rst 10 milliseconds after the merger. Implications for large-scale structu res and jet formation (gamma-ray burst) are discussed.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/10/ END:VEVENT BEGIN:VEVENT SUMMARY:Arthur G. Suvorov (University of Tübingen) DTSTART:20201029T150000Z DTEND:20201029T160000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/11 DESCRIPTION:Title: Building a theory around a given spacetime\n by 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 break-do wn of general relativity in the strong-field regime. Suppose we found tha t some non-Kerr metric describes black holes\; is there a clear way 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 progress ha s been made in that an explicit solution to the inverse problem is found: given a metric\, reconstructed from astrophysical data\, it is shown how a theory can be built around it. The overarching family of theories redu ces to a number of well known cases in some limits\, including scalar-ten sor\, f(R)\, and k-essence theories. Some implications of this finding an d other recent works are discussed.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/11/ END:VEVENT BEGIN:VEVENT SUMMARY:Claudia de Rham (Imperial College London) DTSTART:20201119T100000Z DTEND:20201119T110000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/12 DESCRIPTION:Title: Causality in Curved Spacetimes\nby Claudia d e Rham (Imperial College London) as part of Gravity @ SISSA\n\n\nAbstract\ nI will investigate the propagation of gravitational waves on curved space times within the low energy effective field theory of gravity\, where effe cts from heavy fields are captured by higher dimensional curvature operato rs. I will clarify why a mild level of superluminality is not in contradic tion with causality\, analyticity or Lorentz invariance and show how consi stent gravitational low energy effective theories can self-protect by ensu ring that any time advance and superluminality calculated within the regim e of validity of the effective theory is necessarily unresolvable for such theories. These considerations are particularly relevant for putting cons traints on cosmological and gravitational effective field theories and I w ill provide explicit criteria to be satisfied so as to ensure causality.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/12/ END:VEVENT BEGIN:VEVENT SUMMARY:Sergey Sibiryakov (Perimeter Institute for Theoretical Physics) DTSTART:20201106T130000Z DTEND:20201106T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/13 DESCRIPTION:Title: Quantum gravity with anisotropic scaling: Past\, Present\, Future\nby Sergey Sibiryakov (Perimeter Institute for Theor etical Physics) as part of Gravity @ SISSA\n\n\nAbstract\nI will review th e status of gravity with anisotropic scaling — an approach to quantum gr avity proposed in 2009 by P. Horava and necessitating rejection of the Lor entz invariance as a fundamental symmetry of nature at high energies. Duri ng the last decade this proposal has passed the scrutiny of self-consisten cy and phenomenological viability and was put on firm grounds by the proof that it leads to unitary renormalizable gravity theories. Investigations in lower dimensions have identified ultraviolet complete asymptotically fr ee gravity models\, with preliminary studies indicating that these may als o exist in four dimensions. I will discuss phenomenological challenges to this program and give an outlook of future directions.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/13/ END:VEVENT BEGIN:VEVENT SUMMARY:Jose Maria Ezquiaga (University of Chicago) DTSTART:20201022T140000Z DTEND:20201022T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/14 DESCRIPTION:Title: Cosmology and fundamental physics with binary bl ack-hole mergers\nby Jose Maria Ezquiaga (University of Chicago) as pa rt of Gravity @ SISSA\n\n\nAbstract\nGravitational waves (GWs) from the fi rst two observing runs of LIGO/Virgo have uncovered a population of stella r-mass binary black holes (BBHs). In the first part of the talk\, I will d iscuss the consistency of these observations with the theory of pair insta bility supernova (PISN)\, which predicts a mass gap in the black-hole mass spectrum in the range ~50 -120 Msun. I will then concentrate on the prosp ects of detecting BBHs above the PISN gap. These "far side of the PISN gap " binaries would be ideal multi-band GW sources with promising science. I will show how far-side binaries can become standard sirens\, leave imprint s in the stochastic GW background and might help constraining nuclear reac tion rates. In the second part of the talk\, I will discuss the possibilit y of identifying lensed GWs from BBHs. In particular\, I will focus on the key role of lensing phase shifts. Contrary to electromagnetic radiation i ntuition\, lensing phase shifts could distort the GW waveform so that it d iffers from the (unlensed) general relativity prediction. I will quantify how relevant these distortions are for current GW detectors and signals\, outlining an optimal lensing search strategy. Time permitting\, I will dis cuss tests of general relativity with lensed and unlensed GW events.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/14/ END:VEVENT BEGIN:VEVENT SUMMARY:Diego Blas (King's College London) DTSTART:20201112T100000Z DTEND:20201112T110000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/15 DESCRIPTION:Title: Quenching or detecting BH rotational superradian ces\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 superr adiance: first\, I will describe how BH photon superradiance is typically quenched by interactions of the photon cloud with the ambient electrons. S econd\, I will explain how an axionic cloud may impact the CMB if it decay s into low energy photons which quickly heat and ionise the surrounding me dium to Mpc scales.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/15/ END:VEVENT BEGIN:VEVENT SUMMARY:Andrea Maselli (La Sapienza University) DTSTART:20201126T130000Z DTEND:20201126T140000Z DTSTAMP:20260422T225700Z 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 validity of Einstein's\ntheory in the strong field regime is one of the most ambitious \ngoals of gravitational wave (GW) detectors\, and a primary target\nfor t he space satellite LISA.\n\nAmong binary sources observables by LISA\, ext reme mass ratio inspirals\n(EMRIs) in which a stellar mass object follows hundreds of thousands\nof orbits around a supermassive black hole\, harbou r the potential for\nvery precise tests of gravity.\n\nThis simplest modif ications of General Relativity (GR) predict the\nexistence of scalar field s which modify the gravitational interaction.\nHowever modelling EMRIs 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 will prese nt a new study\, showing that for a vast\nclass of gravity theories\, alte rnative to GR\, the description of\nEMRIs greatly simplifies\, reducing th e problem to the motion of a\nscalar charge around a Kerr black hole. In p articular I will show\nhow all the information on the GR modifications are universally\ncaptured by a single parameter\, the scalar charge of the sm all\nobject. This promises drastic simplifications in terms of waveform\nm odelling\, and offers the opportunity to use EMRIs for agnostic tests\nof General Relativity\, which are independent from the\nunderlying theory of gravity.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/16/ END:VEVENT BEGIN:VEVENT SUMMARY:Lorenzo Annulli (Instituto Superiore Tecnico CENTRA) DTSTART:20201210T130000Z DTEND:20201210T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/17 DESCRIPTION:Title: Stirred and shaken: dynamical behavior of boson stars and dark matter cores\nby Lorenzo Annulli (Instituto Superiore T ecnico CENTRA) as part of Gravity @ SISSA\n\n\nAbstract\nThe nature and pr operties of dark matter are arguably among the most important open issues in science. Interesting candidates for dark matter include light bosonic f ields. Such scalar fields can give rise to confined structures\, as boson stars or Q-balls. Boson stars are interesting hypothetical new "dark matte r stars"\, but also good descriptions of dark matter haloes when the field s are ultralight. In this talk\, I'm going to focus on the dynamical respo nse of Newtonian 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 stabili ty to the way they interact with surrounding objects (stars\, planets or b lack holes etc.). Among others issues\, I am going to describe the local c hanges 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 s tars moving within it\, the flux of energy and momentum induced by coalesc ing binaries\, etc. I will provide a complete picture of the interaction b etween black holes or stars and the ultralight dark matter environment the y live in.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/17/ END:VEVENT BEGIN:VEVENT SUMMARY:Eugeny Babichev (Laboratoire de Physique Théorique d’Orsay (LPT )) DTSTART:20201203T100000Z DTEND:20201203T110000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/18 DESCRIPTION:Title: Disforming the Kerr metric\nby Eugeny Babich ev (Laboratoire de Physique Théorique d’Orsay (LPT)) as part of Gravity @ SISSA\n\n\nAbstract\nI will present a disformal versions of the Kerr sp acetime 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 reaching c onsequences on the structure of the solution. I will discuss properties of three different hypersurfaces in the disformed Kerr metric: the ergospher e\, the stationary limit of infalling observers\, and the event horizon\, as compared to the Kerr metric.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/18/ END:VEVENT BEGIN:VEVENT SUMMARY:Maria Okounkova (Center for Computational Astrophysics\, Flatiron Institute) DTSTART:20201217T140000Z DTEND:20201217T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/19 DESCRIPTION:Title: Binary Black Hole Mergers beyond General Relativ ity\nby Maria Okounkova (Center for Computational Astrophysics\, Flati ron Institute) as part of Gravity @ SISSA\n\n\nAbstract\nAt some length sc ale\, Einstein's theory of general relativity (GR) must break down and be reconciled with quantum mechanics in a quantum theory of gravity. Binary b lack hole mergers probe the strong field\, non-linear\, highly dynamical r egime of gravity\, and thus gravitational waves from these systems could c ontain beyond-GR signatures. While LIGO presently performs model-independe nt and parametrized tests of GR\, in order to perform model-dependent test s\, we must have access to numerical relativity binary black hole waveform predictions in beyond-GR theories through full inspiral\, merger\, and ri ngdown. In this talk\, I will discuss our results in producing full numeri cal relativity waveforms in beyond-GR theories\, including dynamical Chern -Simons gravity and Einstein dilaton Gauss-Bonnet gravity.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/19/ END:VEVENT BEGIN:VEVENT SUMMARY:Christian Wuthrich (University of Geneva) DTSTART:20210114T130000Z DTEND:20210114T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/20 DESCRIPTION:Title: Beyond the limits of analogue experiments\nb y Christian Wuthrich (University of Geneva) as part of Gravity @ SISSA\n\n \nAbstract\nAnalogue experiments have attracted interest for their potenti al to shed light on inaccessible domains. For instance\, ‘dumb holes’ in fluids and Bose–Einstein condensates\, as analogues of black holes\, have been promoted as means of confirming the existence of Hawking radiati on in real black holes. Contra recent claims in the literature\, I have ar gued with Karen Crowther and Niels Linnemann (forthcoming) that analogue e xperiments are not capable of confirming the existence of particular pheno mena in inaccessible target systems such as astrophysical black holes. 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 system when it is precisely this adequacy that is at stake. Evans and Thébault (2020) have very recently identified four problems with our argument. I will dis cuss and hopefully rebut their points\, but also constructively discuss th e similarity of the case of Hawking radiation with that of stellar nucleos ynthesis.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/20/ END:VEVENT BEGIN:VEVENT SUMMARY:Alejandro Cárdenas-Avendaño (Illinois Center for Advanced Studie s of the Universe (iCASU)) DTSTART:20210107T130000Z DTEND:20210107T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/21 DESCRIPTION:Title: Experimental gravity with electromagnetic and gr avitational waves\nby Alejandro Cárdenas-Avendaño (Illinois Center f or Advanced Studies of the Universe (iCASU)) as part of Gravity @ SISSA\n\ n\nAbstract\nOver the past years\, electromagnetic and gravitational obser vations have been used to understand the nature of black holes and the mat erial around them. Our ability to learn about the underlying physics\, how ever\, depends heavily on our understanding of the gravity theory that des cribes the geometry around these compact objects\, and for the electromagn etic observations\, also on the complex astrophysics that produces the obs erved radiation. In this talk\, I will discuss our current ability to cons train and detect deviations from general relativity using (i) the electrom agnetic radiation emitted by an accretion disk around a black hole\, and ( ii) the gravitational waves produced when comparable-mass black holes coll ide\, and when a small compact object falls into a supermassive one in an extreme mass-ratio inspiral. I will also compare the constraining capabili ties of these two types of observations to show how current gravitational wave observations have already placed constraints on possible modification s to general relativity\, that are more stringent than what can be achieve d with current and near-future electromagnetic observations.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/21/ END:VEVENT BEGIN:VEVENT SUMMARY:Frank Ohme (Max Planck Institute) DTSTART:20210121T100000Z DTEND:20210121T110000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/22 DESCRIPTION:Title: The Binary Universe In Gravitational Waves\n by Frank Ohme (Max Planck Institute) as part of Gravity @ SISSA\n\n\nAbstr act\nThe data of two and a half observing runs of the gravitational-wave i nterferometers LIGO and Virgo have been fully analyzed to date. The result s have recently been published in the second transient catalogue\, GWTC-2\ , which contains no fewer than 50 binary merger candidates\, the majority of which are expected to be real astrophysical events. Apart from the shea r number of events\, the most recent observations have added some exciting binaries that further push the boundaries of what we have observed. In th is talk\, I will summarize these most recent findings\, highlighting binar ies that are exceptional from an astrophysical or fundamental physics poin t of view. In addition\, statistical methods become more powerful in extra cting properties of the binary population that becomes more and more visib le in the gravitational-wave universe.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/22/ END:VEVENT BEGIN:VEVENT SUMMARY:Elisa Maggio (Sapienza University of Rome) DTSTART:20210211T130000Z DTEND:20210211T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/23 DESCRIPTION:Title: How does a dark compact object ringdown?\nby Elisa Maggio (Sapienza University of Rome) as part of Gravity @ SISSA\n\n \nAbstract\nGravitational waves from the coalescence of compact binaries p rovide a unique opportunity to test gravity in strong field regime. In par ticular\, the postmerger phase of the gravitational signal is a proxy 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. Such dark compact objects can emit a modified ringdown with respect to the black hol e case and late-time gravitational wave echoes as characteristic fingerpri nts.\nIn this talk\, I develop a generic framework to the study of the rin gdown of dark compact objects and I assess their detectability with curren t and future gravitational-wave detectors.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/23/ END:VEVENT BEGIN:VEVENT SUMMARY:Nicolas Sanchis-Gual (CENTRA) DTSTART:20210128T130000Z DTEND:20210128T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/24 DESCRIPTION:Title: Light in the dark: GW190521 as a Proca star merg er\nby Nicolas Sanchis-Gual (CENTRA) as part of Gravity @ SISSA\n\n\nA bstract\nThe detections of gravitational waves are opening a new window to the\nUniverse. The nature of black holes and neutron stars may now be\nun veiled\, but gravitational radiation may also lead to exciting\ndiscoverie s of new exotic compact objects\, oblivious to electromagnetic\nwaves. In particular\, Advanced LIGO-Virgo recently reported a short\ngravitational- wave signal (GW190521) interpreted as a quasi-circular\nmerger of black ho les\, one at least populating the pair-instability\nsupernova gap. We foun d that GW190521 is also consistent with\nnumerically simulated signals fro m head-on collisions of two (equal mass\nand spin) horizonless vector boso n stars (aka Proca stars). This\nprovides the first demonstration of close degeneracy between these two\ntheoretical models\, for a real gravitation al-wave event.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/24/ END:VEVENT BEGIN:VEVENT SUMMARY:Antoine Lehébel (Instituto Superior Tecnico (IST)) DTSTART:20210225T130000Z DTEND:20210225T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/25 DESCRIPTION:Title: Onset of spontaneous scalarization in generalize d scalar-tensor theories\nby Antoine Lehébel (Instituto Superior Tecn ico (IST)) as part of Gravity @ SISSA\n\n\nAbstract\nSpontaneous scalariza tion is a mechanism that endows relativistic stars and black holes with a nontrivial configuration only when their spacetime curvature exceeds some threshold. Beyond this threshold\, they acquire a nontrivial scalar config uration\, which also affects their structure. The onset of scalarization i s controlled only by terms that contribute to linear perturbation around s olutions of general relativity. I will present the complete set of these t erms in generalized scalar-tensor theories\, and determine the relevant th resholds in terms of the contributing coupling constants and the propertie s of the compact object.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/25/ END:VEVENT BEGIN:VEVENT SUMMARY:William East (Perimeter Institute for Theoretical Physics) DTSTART:20210219T130000Z DTEND:20210219T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/26 DESCRIPTION:Title: Evolving Binary Black Hole Spacetimes Beyond Ein stein\nby William East (Perimeter Institute for Theoretical Physics) a s part of Gravity @ SISSA\n\n\nAbstract\nGravitational wave observations o f black hole and other compact object mergers have given us an unparallele d way to test our understanding of gravity\, and have already been used to constrain a number of possible deviations from general relativity. Howeve r\, despite the success of these observations\, for many alternative theor ies\, it is unclear how to\, or even if one can\, obtain a full theoretica l prediction of what happens\, e.g.\, when two black holes merge. I will d iscuss recent progress in this regard\, showing how full\, non-perturbativ e evolutions of Horndeski theories of gravity can be carried out using a m odified harmonic formulation. Focusing on the particular case of Einstein- scalar-Gauss-Bonnet gravity as a first application\, I will present new re sults on the dynamics of black hole scalarization and the mergers of compa ct objects. These methods can be used to make gravitational wave predictio ns in the strong-field regime\, and to benchmark approximate treatments of deviations from general relativity.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/26/ END:VEVENT BEGIN:VEVENT SUMMARY:Shahin Sheikh Jabbari (Institute for Research in Fundamental Scien ces (IPM)) DTSTART:20210204T090000Z DTEND:20210204T100000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/27 DESCRIPTION:Title: Temperature of Black Holes in Horndeski Gravity Theories\nby Shahin Sheikh Jabbari (Institute for Research in Fundamen tal Sciences (IPM)) as part of Gravity @ SISSA\n\n\nAbstract\nHorndeski th eories are the most general family of scalar-tensor gravity with second or der equations of motion. In these theories speeds of propagation of gravi tons and photons are in general different and gravitons move on an effect ive metric different than the one seen by photons. These theories admit bl ack hole solutions with the peculiar feature that they do not satisfy the first law with the entropy given by the Wald formula. We argue that the is sue with the first law stems from the fact that black hole temperature is not given by the surface gravity of the black hole metric\, but with the s urface gravity of the effective metric seen by gravitons. The modified tem perature\, with the entropy unambiguously computed by the solution phase s pace method\, yields the correct first law. We discuss far-reaching implic ations of our results for black hole thermodynamics beyond the Horndeski t heories\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/27/ END:VEVENT BEGIN:VEVENT SUMMARY:Anna A. Tokareva (University of Jyväskylä\, Finland) DTSTART:20210318T130000Z DTEND:20210318T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/28 DESCRIPTION:Title: Nonlocal self-healing of Higgs inflation\nby Anna A. Tokareva (University of Jyväskylä\, Finland) as part of Gravity @ SISSA\n\n\nAbstract\nHiggs inflation is known to be a minimal extension of the Standard model allowing for the description of the early Universe inflation. This model is considered as an effective field theory since it has a relatively low cutoff scale\, thus requiring further extensions to b e a valid description of the reheating phase. We present a novel approach to the problem of unitarization and UV completion of the Higgs inflation m odel without introducing new massive degrees of freedom. This approach is based on an analytic infinite derivative modification of the Higgs field k inetic term. We construct a unitary non-local UV completion of the origina l Higgs inflation model such that the inflationary stage stays stable with respect to quantum corrections.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/28/ END:VEVENT BEGIN:VEVENT SUMMARY:Steven Liebling (Long Island University) DTSTART:20210304T130000Z DTEND:20210304T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/29 DESCRIPTION:Title: Neutron Stars Colliding with Compact Objects \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 ong oing one on which I hope to get some feedback. The first recent project st udied the effects of a first order\, high density phase transition in the collision of unequal mass neutron star binaries. The second project studie d the multimessenger signals arising from the merger of a black hole--neut ron star binary within an effectively force-free magnetosphere. Finally\, in on-going work\, we consider a somewhat exotic possibility of a magnetiz ed primordial black hole colliding with a neutron star.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/29/ END:VEVENT BEGIN:VEVENT SUMMARY:Miguel Zumalacarregui (Max Planck Institute) DTSTART:20210325T150000Z DTEND:20210325T160000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/30 DESCRIPTION:Title: Gravitational Wave lensing beyond Einstein’s G eneral Relativity\nby Miguel Zumalacarregui (Max Planck Institute) as part of Gravity @ SISSA\n\n\nAbstract\nGravitational lensing of light is a well established test of gravity. However\, little is known about how gra vitational waves (GW) propagate beyond the simplest space-times in theorie s beyond Einstein’s General Relativity (GR). I will present a framework for GW lensing beyond GR at leading order in frequency. The modified causa l structure and kinetic mixing between metric and additional degrees of fr eedom leads to new phenomena\, providing clear-cut tests that do not requi re an electromagnetic counterpart. I will present detailed predictions for static\, spherically symmetric lenses in an quartic Horndeski theory in w hich novel GW lensing effects can provide tests far more stringent than th e multi-messenger event GW170817. The next terms in the frequency expansio n will further enrich the phenomenology of GW lensing and enable new preci sion tests of gravity.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/30/ END:VEVENT BEGIN:VEVENT SUMMARY:Felix-Louis Julie (Johns Hopkins University) DTSTART:20210311T153000Z DTEND:20210311T163000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/31 DESCRIPTION:Title: Gravitational radiation from a binary black hole coalescence in Einstein-scalar-Gauss-Bonnet gravity\nby Felix-Louis J ulie (Johns Hopkins University) as part of Gravity @ SISSA\n\n\nAbstract\n In this talk I will show how to derive analytic gravitational waveforms as sociated to the coalescence of a “hairy” black hole binary in Einstein -scalar-Gauss-Bonnet gravity (ESGB). I will present the associated post-Ne wtonian (PN) Lagrangian and gravitational wave fluxes. The PN framework re lies on reducing the black holes to point particles with scalar-field-depe ndent masses. In light of the first law of thermodynamics of ESGB black ho les\, I will show that this procedure amounts to fixing their Wald entropi es. As a consequence\, inspiraling ESGB black holes can slowly grow scalar “hair” until they turn into naked singularities. I will then extend t he scope of the PN approximation to the strong field regime near merger by generalizing the Effective-One-Body (EOB) formalism to ESGB gravity.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/31/ END:VEVENT BEGIN:VEVENT SUMMARY:Salvatore Vitale (MIT Kavli Institute) DTSTART:20210409T120000Z DTEND:20210409T130000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/32 DESCRIPTION:Title: Physics and astrophysics with gravitational wave s\nby Salvatore Vitale (MIT Kavli Institute) as part of Gravity @ SISS A\n\n\nAbstract\nFive years after the first direct detection of gravitatio nal waves\, over 50 compact binary mergers have been discovered in the dat a of the LIGO and Virgo detectors. The masses and spins of these compact o bjects can be used to tackle multiple problems in physics\, astrophysics a nd cosmology. In this talk I will first discuss what can be learned about the properties of the individual gravitational-wave sources\, and how the results depend on some of the analysis details\, such as Bayesian priors a nd noise treatment. I will then discuss what can be learned from the over all set of detections. As an example\, I will report on recent constraints on the existence of ultralight scalar bosons obtained using the latest LI GO/Virgo data release.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/32/ END:VEVENT BEGIN:VEVENT SUMMARY:Sébastien Renaux-Petel (Institut Astrophysique de Paris) DTSTART:20210401T120000Z DTEND:20210401T130000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/33 DESCRIPTION:Title: Probing primordial features with the Stochastic Gravitational Wave Background\nby Sébastien Renaux-Petel (Institut As trophysique de Paris) as part of Gravity @ SISSA\n\n\nAbstract\nFeatures o f the primordial density fluctuations power spectrum are theoretically ext remely motivated and detecting them would provide a unique insight into th e physics of the early universe. In this talk\, I will show how the stocha stic gravitational wave background (SGWB) offers a new way to probe primor dial features\, on small scales complementary to the ones probed by the Co smic Microwave Background and large scale structure observations. These fe atures give rise to specific oscillatory patterns in the frequency profile of the SGWB\, which can be detected in future GW observatories like LISA. \n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/33/ END:VEVENT BEGIN:VEVENT SUMMARY:Andreas Mantziris (Imperial College London) DTSTART:20210415T120000Z DTEND:20210415T130000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/34 DESCRIPTION:Title: Cosmological implications of electroweak vacuum instability: constraints on the Higgs curvature coupling from inflation\nby Andreas Mantziris (Imperial College London) as part of Gravity @ SIS SA\n\n\nAbstract\nThe current experimentally measured parameters of the St andard Model (SM) suggest that our universe lies in a metastable electrowe ak vacuum\, where the Higgs field could decay to a lower vacuum state with catastrophic consequences. Our measurements dictate that such an event ha s not happened yet\, despite the many different mechanisms that could have triggered it during our past light-cone. Via this observation\, we can es tablish a promising link between cosmology and particle physics and thus c onstrain important parameters of our theories. The focus of our work has b een to explore this possibility by calculating the probability of the fals e vacuum to decay during the period of inflation and using it to constrain the last unknown renormalisable SM parameter $\\xi$\, which couples the H iggs field with space-time curvature. In our latest study\, we derived low er bounds for the Higgs-curvature coupling from vacuum stability in three inflationary models: quadratic and quartic chaotic inflation\, and Starobi nsky-like power-law inflation. In contrast to most previous studies\, we t ook the time-dependence of the Hubble rate into account both in the geomet ry of our past light-cone and in the Higgs effective potential\, which is approximated with three-loop renormalisation group improvement supplemente d with one-loop curvature corrections. We find that in all three models\, the lower bound is $\\xi \\gtrsim 0.051 ... 0.066$ depending on the top qu ark mass. We also demonstrated that vacuum decay is most likely to happen a few e-foldings before the end of inflation.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/34/ END:VEVENT BEGIN:VEVENT SUMMARY:Dominik Schleicher (University of Concepción) DTSTART:20210527T120000Z DTEND:20210527T130000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/35 DESCRIPTION:Title: Formation of the first supermassive black holes< /a>\nby Dominik Schleicher (University of Concepción) as part of Gravity @ SISSA\n\n\nAbstract\nFor the origin of the first supermassive black hole s in the Universe\, different scenarios have been proposed\, ranging from the direct collapse of massive gas clouds into one single object\, run-awa y collisions in very dense stellar clusters\, as well as accretion of init ially stellar-mass black holes. In this talk I will present progress from the last several years in these different scenarios\, starting with system atic tests of the direct collapse scenario and the conditions under which it is feasible. I will also discuss the possibility to have purely colliso n-based scenarios and their possible problems. Finally\, I will present a new mixed scenario where the formation of a massive object is due to the i nterplay of collisions and accretions\, including new results from recent numerical simulations.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/35/ END:VEVENT BEGIN:VEVENT SUMMARY:Valeriya Korol (University of Birmingham) DTSTART:20210610T120000Z DTEND:20210610T130000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/36 DESCRIPTION:Title: Galactic Astronomy with LISA\nby Valeriya Ko rol (University of Birmingham) as part of Gravity @ SISSA\n\n\nAbstract\nW hite dwarf stars are a well-established tool for studying the Milky Way.\n Two white dwarfs in a tight orbit forming a double white dwarf (DWD)\nbina ry offer to us an additional messenger - gravitational waves - for\nexplo ring the Galaxy and its immediate surroundings. Gravitational waves\nprodu ced by DWDs can be detected by the future Laser Interferometer Space\nAnte nna (LISA). I will discuss what we will learn about our Galaxy from\nthe L ISA sample of DWDs. In particular\, I will demonstrate how well the\ndensi ty distribution of DWDs constrains scale parameters of the Milky\nWay's bu lge\, disc and central bar. Finally\, I will show that massive\nGalactic satellites can be seen in the gravitational wave sky and I will\npresent w hich of their properties we will be able to investigate with\nLISA.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/36/ END:VEVENT BEGIN:VEVENT SUMMARY:Macarena Lagos (Columbia University) DTSTART:20210512T120000Z DTEND:20210512T130000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/37 DESCRIPTION:Title: Interacting Gravitational Waves\nby Macarena Lagos (Columbia University) as part of Gravity @ SISSA\n\n\nAbstract\nGra vitational waves (GWs) allow us to probe the content of the Universe and t he behaviour of gravity on cosmological scales\, through information conta ined in their propagation. For instance\, the presence of dynamical fields interacting non-minimally with gravity may induce a non-trivial propagati on of GWs\, changing their propagation speed\, dispersion relation\, or de tected amplitude\, among others. In this talk\, I will discuss particular cosmological scenarios where GWs interact with another tensor field\, such as in the theory of massive bigravity. I will illustrate explicitly how t he GW signal from a coalescence of black holes gets distorted during propa gation\, generating specific features such as echoes of the GW signal emit ted. These strong features suggest that stringent constraints on interacti ng GWs can be placed with current and future GW detectors.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/37/ END:VEVENT BEGIN:VEVENT SUMMARY:Christopher Berry (Northwestern University) DTSTART:20210520T120000Z DTEND:20210520T130000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/38 DESCRIPTION:Title: On the origin of binary black holes\nby Chri stopher Berry (Northwestern University) as part of Gravity @ SISSA\n\n\nAb stract\nGravitational-wave astronomy provides a unique insight into the li ves of black holes. Since the beginning of the advanced-detector era in 20 15\, we have observed gravitational waves from over 40 binary black hole s ystems. Using the measured gravitational-wave signals we can infer the pro perties of their source systems\, and uncover new insights about their for mation. There are currently many mysteries around how massive stars evolve and binaries form in order to create the population of binary black holes . I will explain how we can use the growing catalogue of gravitational-wav e observations to unravel these mysteries and review our discoveries to da te.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/38/ END:VEVENT BEGIN:VEVENT SUMMARY:Marija Tomasevic (University of Barcelona) DTSTART:20210603T120000Z DTEND:20210603T130000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/39 DESCRIPTION:Title: Time in traversable wormholes\nby Marija Tom asevic (University of Barcelona) as part of Gravity @ SISSA\n\n\nAbstract\ nThe last couple of years have greatly illuminated the underlying physics of traversable wormholes. We now know how to construct such solutions with the help of certain quantum effects\, and a more precise connection betwe en wormholes and entanglement is just beginning to emerge. However\, older work indicates that these solutions must either allow for seemingly patho logical behavior\, namely that of generic time machine creation\, or resor t to unknown quantum gravity effects that would prevent such pathologies. Here we will show how simple\, low-energy arguments are enough to make tim e travel (at least) via wormholes impossible.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/39/ END:VEVENT BEGIN:VEVENT SUMMARY:Pedro Cunha (Max Planck Institute) DTSTART:20210624T120000Z DTEND:20210624T130000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/40 DESCRIPTION:Title: Constraining ultralight scalar fields around the M87 black hole using the EHT shadow\nby Pedro Cunha (Max Planck Insti tute) as part of Gravity @ SISSA\n\n\nAbstract\nHypothetical ultralight bo sonic fields will spontaneously form macroscopic bosonic halos around Kerr black holes\, via superradiance\, transferring part of the mass and angul ar momentum of the black hole into the halo. Such a process\, however\, is only efficient if resonant: when the Compton wavelength of the field appr oximately matches the gravitational scale of the black hole. For a complex -valued field\, the process can form a stationary\, bosonic field-black ho le equilibrium state - a black hole with synchronised hair. For sufficient ly massive black holes\, such as the one at the centre of the M87 supergia nt elliptical galaxy\, the hairy black hole can be robust against its own superradiant instabilities\, within a Hubble time. Studying the shadows of such scalar hairy black holes\, we can constrain the amount of hair which is compatible with the Event Horizon Telescope (EHT) observations of the M87 supermassive black hole\, assuming the hair is a condensate of ultrali ght scalar particles of mass ∼1E−20 eV\, as to be dynamically viable. We show the EHT observations set a weak constraint\, in the sense that typ ical hairy black holes that could develop their hair dynamically\, are com patible with the observations\, when taking into account the EHT error bar s and the black hole mass/distance uncertainty. We will also discuss a re cent theorem establishing that an equilibrium Black Hole must admit\, unde r generic conditions\, at least one circular Light Ring orbit outside the horizon. The proof relies on a topological argument and makes virtually no assumptions on the matter content or gravity model.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/40/ END:VEVENT BEGIN:VEVENT SUMMARY:Maximilliano Isi (MIT Kavli Institute) DTSTART:20210618T120000Z DTEND:20210618T130000Z DTSTAMP:20260422T225700Z 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 carried out the first half of their third observing run from April through October\, 2 019. During this period\, they collected 39 new detections of compact bina ry coalescences\, compiled in the second LIGO-Virgo catalog (GWTC-2). Thes e and previous signals contain invaluable information about the nature of gravity\, which can be used to learn about black holes and test general re lativity. In this talk\, I will provide an overview of these efforts\, wit h a special focus on probes of black hole ringdowns. I will first summariz e and contextualize recent results\, and then close by outlining some of t he open questions and challenges that make this a vibrant field of researc h.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/41/ END:VEVENT BEGIN:VEVENT SUMMARY:Stephen Green (Max Planck Institute for Gravitational Physics) DTSTART:20210506T110000Z DTEND:20210506T120000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/43 DESCRIPTION:Title: Simulation-based inference for compact binaries< /a>\nby Stephen Green (Max Planck Institute for Gravitational Physics) as part of Gravity @ SISSA\n\n\nAbstract\nOver the past five years\, LIGO and Virgo have published 50 detections of gravitational waves from compact bi nary coalescences. To determine the properties of the astrophysical source s\, Bayes’ theorem is typically combined with an iterative sampling algo rithm such as MCMC to draw samples from the posterior—by repeatedly gene rating waveforms and comparing to measured strain data—a process that ta kes from hours to weeks for a single event. In this talk\, I will describe a radically different approach\, using simulation-based inference with de ep neural networks to learn a non-iterative surrogate model for the poster ior. After training on simulated data\, I will show that these networks ca n accurately analyze real binary black holes in seconds\, with results nea rly indistinguishable from standard algorithms. This approach therefore re presents a path to faster multimessenger alerts and a means to address the growing rate of detections. I will conclude by discussing prospects for m oving beyond standard algorithms not just in terms of speed\, but in accur acy as well.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/43/ END:VEVENT BEGIN:VEVENT SUMMARY:Christian Krüger (University of Tübingen) DTSTART:20211026T130000Z DTEND:20211026T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/44 DESCRIPTION:Title: Fast Rotating Neutron Stars: Spectra and Stabili ty without Approximation\nby Christian Krüger (University of Tübinge n) as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/44/ END:VEVENT BEGIN:VEVENT SUMMARY:Matteo Bonetti (University of Milan Bicocca) DTSTART:20211109T140000Z DTEND:20211109T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/45 DESCRIPTION:Title: The massive black hole binary path to coalescenc e\nby Matteo Bonetti (University of Milan Bicocca) as part of Gravity @ SISSA\n\n\nAbstract\nMassive black hole binaries (MBHBs) are expected to form at the centre of merging galaxies during the hierarchical assembly o f the cosmic structure and are expected to be the loudest sources of gravi tational waves (GWs) in the low frequency domain surveyed by the ongoing P ulsar Timing Array (PTA) campaigns and by the forthcoming LISA observatory .\nA meaningful assessment of the detection prospects of the above experim ents critically depends on the abundance and properties of MBHBs that form and evolve during the cosmic history. Therefore\, understanding the MBH d ynamical evolution before and after these binaries form is of paramount im portance.\nIn this talk I will review the current understanding of MBHB ev olution by analysing the several dynamical processes driving MBHBs at diff erent scales and highlighting possible evolutionary bottlenecks that may a rise along their path to coalescence.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/45/ END:VEVENT BEGIN:VEVENT SUMMARY:Alexander Vikman (CEICO) DTSTART:20211130T140000Z DTEND:20211130T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/46 DESCRIPTION:Title: Frozen Axions and Global Dynamics for Newton and Planck\nby Alexander Vikman (CEICO) as part of Gravity @ SISSA\n\n\nA bstract\nI will discuss scale-free Einstein equations\, recently introduce d in e-Print: 2011.07055\, where the information from their trace part is lost. These equations are classically equivalent to General Relativity\, y et the Newton constant becomes a constant of integration or a global dynam ical degree of freedom. Thus\, from the point of view of standard quantiza tion\, this effective Newton constant is susceptible to quantum fluctuatio ns. This is similar to what happens to the cosmological constant in unimod ular gravity where the trace part of the Einstein equations is lost in a d ifferent way. Using analogy with the Henneaux-Teitelboim covariant action for unimodular gravity\, we consider different general-covariant actions r esulting in these dynamics. This setup allows one to formulate the Heisenb erg uncertainty relations for the Newton constant and canonically conjugat ed quantities. Interestingly\, a quasiclassical description in these globa l theories requires a minimal level of quantum fluctuations of the Newton constant in the same way as cosmological constant has a minimal level of q uantum fluctuations in the unimodular gravity\, see e-Print: 2107.09601. U nexpectedly\, one of such theories also promotes Planck's quantum constant to a global degree of freedom\, which is subject to quantum fluctuations. \nFollowing analogy with the unimodular gravity\, we discuss non-covarian t "unimatter" and "unicurvature" gravities describing the scale-free Einst ein equations. Finally\, we show that in some limit of the Yang-Mills gaug e theory a "frozen" axion-like field can emulate not only the cosmological constant\, but also the gravitational Newton constant or even of the quan tum Planck constant.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/46/ END:VEVENT BEGIN:VEVENT SUMMARY:Alexander Vikman (CEICO) DTSTART:20211202T090000Z DTEND:20211202T100000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/47 DESCRIPTION:Title: Dark Matter via Inverse Phase Transition: going beyond freeze-in with observable Gravitational Waves\nby Alexander Vik man (CEICO) as part of Gravity @ SISSA\n\n\nAbstract\nI will discuss a rec ently proposed class of models where Dark Matter (DM) is produced via an i nverse phase transition. The inverse phase transition can be caused by cou pling to some cosmological field. For instance\, this field can be the Ric ci 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-Pr int: 2104.13722. In this most recent work DM is modelled as a real scalar\ , which interacts with the hot primordial plasma through a portal coupling to another scalar field. For a particular sign of the coupling\, this sys tem exhibits an inverse phase transition. The latter leads to an abundant DM production\, even if the portal interaction is so weak that the freeze- in mechanism is inefficient. The model predicts domain wall formation in t he early Universe\, long before the inverse phase transition. These domain walls have a tension decreasing with time\, and completely disappear at t he inverse phase transition\, so that the problem of overclosing the Unive rse is avoided. The domain wall network emits gravitational waves with cha racteristics defined by those of DM. In particular\, the peak frequency of gravitational waves (GW) is determined by the portal coupling constant. F or some range of parameters of the model these GW fall in the observable r ange for currently planned gravitational wave detectors.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/47/ END:VEVENT BEGIN:VEVENT SUMMARY:Laura Bernard (Laboratoire Univers et Théories (LUTH)) DTSTART:20220111T140000Z DTEND:20220111T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/48 DESCRIPTION:Title: Some aspects of gravitational wave modelling in general relativity and scalar-tensor theories\nby Laura Bernard (Labor atoire Univers et Théories (LUTH)) as part of Gravity @ SISSA\n\n\nAbstra ct\nSince the first gravitational wave (GW) detection by the LIGO-Virgo co llaboration\, we have now detected more than fifty GW signals from compact binary systems (made of black hole or neutron stars). In the future\, the LISA space-based interferometer and the next generation detectors\, such as the Einstein Telescope\, will allow to test our gravitational paradigm with an unprecedented precision. One of the new challenge to analysis the forthcoming huge amount of data resides in the high precision modelling of GWs both in general relativity (GR) and beyond. In this talk\, I will foc us on the post-Newtonian method that is used to describe the inspiral phas e of the coalescence of compact binary systems. After reviewing the multip olar - post Minkowskian - post Newtonian formalism and the state-of-the-ar t in GR\, I will explain how such a formalism can be simply applied to sca lar- tensor theories of gravity. In particular\, I will focus on the main phenomenological differences from GR and present the latest developments\, including the contribution from the scalar dipolar tidal effect.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/48/ END:VEVENT BEGIN:VEVENT SUMMARY:Adrien Kuntz (Scuola Normale Superiore) DTSTART:20220929T130000Z DTEND:20220929T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/49 DESCRIPTION:Title: Three-body problem in General Relativity\nby Adrien Kuntz (Scuola Normale Superiore) as part of Gravity @ SISSA\n\nLec ture held in 132.\n\nAbstract\nThree-body systems are very common in the u niverse and it is likely that future gravitational-wave detectors will det ect them and measure their parameters. I will introduce a new approach ("E ffective Two-Body") perturbatively solving the motion of hierarchical thre e-body systems by relying on the existence of two expansion parameters: sm all velocities and large separation of the third body. I will show how thi s new EFT formulation allows to compute the relativistic Hamiltonian of th ree-body systems order-by-order\, and I will present some applications to long-term evolution of three-body systems and waveform modelling.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/49/ END:VEVENT BEGIN:VEVENT SUMMARY:Joao Rosa (Tartu University) DTSTART:20221005T130000Z DTEND:20221005T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/50 DESCRIPTION:Title: Observational signatures of isotropically emitti ng sources orbiting bosonic stars\nby Joao Rosa (Tartu University) as part of Gravity @ SISSA\n\nLecture held in 138.\n\nAbstract\nPushed by a n umber of advances\, electromagnetic observatories have now reached the hor izon scale of supermassive black holes. The existence and properties of ho rizons in our universe is one of the outstanding fundamental issues that c an now be addressed. Here we investigate the ability to discriminate betwe en black holes and compact\, horizonless objects\, focusing on the lensing of hot spots and accretion disks around compact objects. We work in parti cular with boson and Proca stars as central objects\, and show that the ab sence of a horizon gives rise to a characteristic feature -- photons that plough through the central object and produce an extra image. This feature should be universal for central objects made of matter weakly coupled to the standard model.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/50/ END:VEVENT BEGIN:VEVENT SUMMARY:Boris Goncharov (Gran Sasso Science Institute (GSSI)) DTSTART:20221012T130000Z DTEND:20221012T140000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/51 DESCRIPTION:Title: A recipe for detecting the gravitational-wave ba ckground with pulsar timing arrays\nby Boris Goncharov (Gran Sasso Sci ence Institute (GSSI)) as part of Gravity @ SISSA\n\nLecture held in 138.\ n\nAbstract\nWhen galaxies merge\, supermassive black holes at their centr es form binaries. The binaries that are brought together to separations be low ~ 0.1 parsec are expected to experience an adiabatic inspiral dominate d by gravitational wave emission. The detection of these signals is a prim ary goal of pulsar timing arrays (PTA). These experiments observe millisec ond pulsars that act as very precise clocks scattered around our galaxy. I t is expected that the stochastic superposition of supermassive black hole binaries will form a background signal that will be detected prior to ind ividually-resolved sources. Interestingly\, PTAs might now be seeing a spa tially-uncorrelated component of the gravitational-wave background. This i s 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 outline the main ingredients necessary to detect the gravitational-wave background\, t he flavors it may have\, and the new science it may bring to the table.\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/51/ END:VEVENT BEGIN:VEVENT SUMMARY:Stefano Rinaldi (University of Pisa) DTSTART:20221116T140000Z DTEND:20221116T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/52 DESCRIPTION:by Stefano Rinaldi (University of Pisa) as part of Gravity @ S ISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/52/ END:VEVENT BEGIN:VEVENT SUMMARY:Mario Herrero-Valea (Juan de la Cierva) DTSTART:20221123T140000Z DTEND:20221123T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/53 DESCRIPTION:by Mario Herrero-Valea (Juan de la Cierva) as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/53/ END:VEVENT BEGIN:VEVENT SUMMARY:Enrico Barausse DTSTART:20240111T140000Z DTEND:20240111T160000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/54 DESCRIPTION:Title: Gravitational Waves / Room 135\nby Enrico Ba rausse as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/54/ END:VEVENT BEGIN:VEVENT SUMMARY:Ramit Dey DTSTART:20240118T133000Z DTEND:20240118T143000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/62 DESCRIPTION:Title: Online APP Seminar Host: Stefano Liberati\nb y Ramit Dey as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/62/ END:VEVENT BEGIN:VEVENT SUMMARY:Tim Linden DTSTART:20240208T133000Z DTEND:20240208T143000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/94 DESCRIPTION:Title: APP Seminar\nby Tim Linden as part of Gravit y @ SISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/94/ END:VEVENT BEGIN:VEVENT SUMMARY:Arianna Renzini DTSTART:20240118T090000Z DTEND:20240118T100000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/95 DESCRIPTION:Title: Room 128: Searching for Gravitational-wave Backg rounds: targets\, methods\, and broad implications\nby Arianna Renzini as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/95/ END:VEVENT BEGIN:VEVENT SUMMARY:Stefano Ascenzi DTSTART:20240119T090000Z DTEND:20240119T100000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/96 DESCRIPTION:Title: Room 128: Gamma-ray bursts and neutron stars in the multimessenger era\nby Stefano Ascenzi as part of Gravity @ SISSA\ n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/96/ END:VEVENT BEGIN:VEVENT SUMMARY:Silvia Celli DTSTART:20240123T090000Z DTEND:20240123T100000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/97 DESCRIPTION:Title: Room 128: Supernova remnants and star clusters a s candidate cosmic-ray accelerators\nby Silvia Celli as part of Gravit y @ SISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/97/ END:VEVENT BEGIN:VEVENT SUMMARY:Jieshuang Wang DTSTART:20240125T140000Z DTEND:20240125T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/98 DESCRIPTION:Title: Room 128: Multi-messenger astrophysics: neutron star mergers and active galactic nucleus jet\nby Jieshuang Wang as par t of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/98/ END:VEVENT BEGIN:VEVENT SUMMARY:Alessia Franchini DTSTART:20240215T090000Z DTEND:20240215T100000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/99 DESCRIPTION:Title: APP Seminar/ Room 128: Electromagnetic emission from gravitational waves sources\nby Alessia Franchini as part of Grav ity @ SISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/99/ END:VEVENT BEGIN:VEVENT SUMMARY:Chantal Laure Pitte (SISSA) DTSTART:20241205T133000Z DTEND:20241205T150000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/100 DESCRIPTION:Title: LISA and the No-Hair Theorem: Efforts Towards P recision Tests\nby Chantal Laure Pitte (SISSA) as part of Gravity @ SI SSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/100/ END:VEVENT BEGIN:VEVENT SUMMARY:Marina De Amicis (Niels Bohr Institute) DTSTART:20241216T133000Z DTEND:20241216T143000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/101 DESCRIPTION:Title: A fairy-TAIL story\nby Marina De Amicis (Ni els Bohr Institute) as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/101/ END:VEVENT BEGIN:VEVENT SUMMARY:Ricardo Della Monica (Universidad de Salamanca) DTSTART:20241219T133000Z DTEND:20241219T143000Z DTSTAMP:20260422T225700Z UID:GeneralRelativityandModifiedGrav/102 DESCRIPTION:Title: -\nby Ricardo Della Monica (Universidad de Salamanca) as part of Gravity @ SISSA\n\nAbstract: TBA\n LOCATION:https://researchseminars.org/talk/GeneralRelativityandModifiedGra v/102/ END:VEVENT END:VCALENDAR