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Speaker: Nikolaos AthanasiouTitle: Formation of trapped surfaces in the Einstein-Yang-Mills systemVenue: virtualGeneral Relativity Seminar Speaker: Nikolaos Athanasiou (University of Crete, Greece) Title: Formation of trapped surfaces in the Einstein-Yang-Mills system Abstract: The purpose of this talk is to give an overview of a semi-global existence result and a trapped surface formation results in the context of the Einstein-Yang-Mills system. Adopting a “signature for decay rates” approach first introduced by An, we develop a novel gauge (and scale) invariant hierarchy of non-linear estimates for the Yang-Mills curvature which, together with the estimates for the gravitational degrees of freedom, yield the desired semi-global existence result. Once semi-global existence has been established, we will explain how the formation of a trapped surface follows from a standard ODE argument. This is joint… |
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Speaker: Kwinten FransenTitle: Quasinormal Modes from Penrose LimitsVenue: CMSA Room G10General Relativity Seminar Speaker: Kwinten Fransen (UC Santa Barbara) Title: Quasinormal Modes from Penrose Limits Abstract: In this talk, I will explain how to describe quasinormal modes with large real frequencies using Penrose limits. To do so, I first recall relevant aspects of the Penrose limit, and its resulting plane wave spacetimes, as well as quasinormal modes to subsequently tie these together. Having established the main principle, I will illustrate the usefulness of this point of view with the geometric realization of the emergent symmetry algebra underlying the quasinormal modes in the large real frequency limit and present its application to the astrophysically important example of Kerr black holes. Based on arXiv:2301.06999. |
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Speaker: Maciej ZworskiTitle: Quasinormal modes and Ruelle resonances: mathematician’s perspectiveVenue: CMSA Room G10General Relativity Seminar Speaker: Maciej Zworski, UC Berkeley Title: Quasinormal modes and Ruelle resonances: mathematician’s perspective Abstract: Quasinormal modes of gravitational waves and Ruelle resonances in hyperbolic classical dynamics share many general properties and can be considered “scattering resonances”: they appear in expansions of correlations, as poles of Green functions and are associated to trapping of trajectories (and are both notoriously hard to observe in nature, unlike, say, quantum resonances in chemistry or scattering poles in acoustical scattering). I will present a mathematical perspective that also includes zeros of the Riemann zeta function (scattering resonances for the Hamiltonian given by the Laplacian on the modular surface) and stresses the importance of different kinds of trapping phenomena, resulting,… |
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Speaker: Chiara ToldoTitle: Near extremal de Sitter black holes and JT gravityVenue: virtualGeneral Relativity Seminar Speaker: Chiara Toldo (Harvard) Title: Near extremal de Sitter black holes and JT gravity Abstract: In this talk I will explore the thermodynamic response near extremality of charged black holes in four-dimensional Einstein-Maxwell theory with a positive cosmological constant. The latter exhibit three different extremal limits, dubbed cold, Nariai and ultracold configurations, with different near-horizon geometries. For each of these three cases I will analyze small deformations away from extremality, and construct the effective two-dimensional theory, obtained by dimensional reduction, that captures these features. The ultracold case in particular shows an interesting interplay between the entropy variation and charge variation, realizing a different symmetry breaking with respect to the other two near-extremal limits. |
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Speaker: Prashant KocherlakotaTitle: Testing spacetime geometry with images of supermassive compact objects: Current status and the futureVenue: virtualGeneral Relativity Seminar Speaker: Prashant Kocherlakota (BHI) Title: Testing spacetime geometry with images of supermassive compact objects: Current status and the future Abstract: Astrophysical black holes (BHs) are expected to be described by the Kerr solution of the Einstein equations. Several frameworks have recently been developed to parametrically deform the Kerr metric in significantly different ways, to enable formulations of tests of the no-hair theorems. Testing the viability status of alternative models – such as non-Kerr BHs from general relativity, BHs from alternative theories, wormholes, and other exotic objects – as descriptors of astrophysical objects has been of longstanding interest. The Event Horizon Telescope (EHT) recently imaged Sagittarius A* (Sgr A*), the supermassive compact object at the… |
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Speaker: Allen FangTitle: A new proof for the nonlinear stability of slowly-rotating Kerr-de SitterVenue: virtualGeneral Relativity Seminar Speaker: Allen Fang (Princeton) Title: A new proof for the nonlinear stability of slowly-rotating Kerr-de Sitter Abstract: The nonlinear stability of the slowly-rotating Kerr-de Sitter family was first proven by Hintz and Vasy in 2016 using microlocal techniques. In my talk, I will present a novel proof of the nonlinear stability of slowly-rotating Kerr-de Sitter spacetimes that avoids frequency-space techniques outside of a neighborhood of the trapped set. The proof uses vector field techniques to uncover a spectral gap corresponding to exponential decay at the level of the linearized equation. The exponential decay of solutions to the linearized problem is then used in a bootstrap proof to conclude nonlinear stability. |
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Speaker: Semyon DyatlovTitle: Ringdown and geometry of trapping for black holesVenue: HybridGeneral Relativity Seminar Speaker: Semyon Dyatlov (MIT) Title: Ringdown and geometry of trapping for black holes Abstract: Quasi-normal modes are complex exponential frequencies appearing in long time expansions of solutions to linear wave equations on black hole backgrounds. They appear in particular during the ringdown phase of a black hole merger when the dynamics is expected to be driven by linear effects. In this talk I give an overview of various results in pure mathematics which relate asymptotic behavior of quasi-normal modes at high frequency to the geometry of the set of trapped null geodesics, such as the photon sphere in Schwarzschild (-de Sitter). These trapped geodesics have two kinds of behavior: the geodesic flow is hyperbolic in directions normal… |
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Speaker: Pierre HeidmannTitle: Schwarzschild-like Topological Solitons in GravityVenue: virtualGeneral Relativity Seminar Speaker: Pierre Heidmann (Johns Hopkins) Title: Schwarzschild-like Topological Solitons in Gravity Abstract: We present large classes of non-extremal solitons in gravity that are asymptotic to four-dimensional Minkowski spacetime plus extra compact dimensions. They correspond to smooth horizonless geometries induced by topology in spacetime and supported by electromagnetic flux, which characterize coherent states of quantum gravity. We discuss a new approach to deal with Einstein-Maxwell equations in more than four dimensions, such that they decompose into a set of Ernst equations. We generate the solitons by applying different techniques associated with the Ernst formalism. We focus on solitons with zero net charge yet supported by flux, and compare them to Schwarzschild black holes. These are also ultra-compact geometries with very high redshift but… |
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Speaker: Pengyu LeTitle: Asymptotic geometry of null hypersurface in Schwarzschild spacetime and null Penrose inequalityVenue: virtualGeneral Relativity Seminar Speaker: Pengyu Le (BIMSA) Title: Asymptotic geometry of null hypersurface in Schwarzschild spacetime and null Penrose inequality Abstract: Null Penrose inequality is an important case of the well-known Penrose inequality on a null hypersurface. It conjectures the relation between the area of the outmost marginally trapped surface and the Bondi mass at null infinity. Following the proposal of Christodoulou and Sauter, we employ the perturbation method to study the asymptotic geometry of null hypersurfaces at null infinity in a perturbed vacuum Schwarzshild spacetime. We explain how to apply this perturbation theory to prove null Penrose inequality on a nearly spherically symmetric null hypersurface in a perturbed vacuum Schwarzschild spacetime. |
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Speaker: Naqing XieTitle: Gravitational Wave, Angular Momentum, and Supertranslation AmbiguityVenue: virtualGeneral Relativity Seminar Speaker: Naqing Xie (Fudan University) Title: Gravitational Wave, Angular Momentum, and Supertranslation Ambiguity Abstract: The supertranslation ambiguity of angular momentum is a long-standing and conceptually important issue in general relativity. Recently, there appeared the first definition of angular momentum at null infinity that is supertranslation invariant. However, in the compact binary coalescence community, supertranslation ambiguity is often ignored. We have shown that, in the linearised theory of gravitational wave, the new angular momentum coincides with the classical definition at the quadrupole level. This talk is based on a recent joint work with Xiaokai He and Xiaoning Wu. |
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Speaker: Sergei DubovskyTitle: Love Symmetry of Black HolesVenue: CMSA Room G10General Relativity Seminar Speaker: Sergei Dubovsky (New York University) Title: Love Symmetry of Black Holes Abstract: Perturbations of massless fields in the Kerr-Newman black hole background enjoy a (“Love”) SL(2,ℝ) symmetry in the suitably defined near zone approximation. We show how the intricate behavior of black hole responses in four and higher dimensions can be understood from the SL(2,ℝ) representation theory. In particular, static perturbations of four-dimensional black holes belong to highest weight SL(2,ℝ) representations. It is this highest-weight property that forces the static Love numbers to vanish. We show that the Love symmetry is tightly connected to the enhanced isometries of extremal black holes. The Love symmetry also exhibits a peculiar UV/IR mixing. |
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Speaker: Oscar DiasTitle: Strong Cosmic CensorshipVenue: virtualGeneral Relativity Seminar Speaker: Professor Oscar Dias (University of Southampton) Title: Strong Cosmic Censorship Abstract: Generically, strong cosmic censorship (SCC) is the statement that physics within general relativity should be predicted from initial data prescribed on a Cauchy hypersurface. In this talk I will review how fine-tuned versions of SCC have been formulated and evolved along the last decades up to the point where we believe that Christodoulou’s version is true in asymptotically flat spacetimes. However, I will also describe that in recent years it was found that this is no longer necessarily true for some other backgrounds, namely in some de Sitter (with a positive cosmological constant) spacetimes or even in rotating BTZ black holes in 3-dimensional Anti-de Sitter… |
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Speaker: Uri KolTitle: Duality in Einstein’s GravityVenue: CMSA Room G10General Relativity Seminar Speaker: Uri Kol, CMSA Title: Duality in Einstein’s Gravity Abstract: Electric-Magnetic duality has been a key feature behind our understanding of Quantum Field Theory for over a century. In this talk I will describe a similar property in Einstein’s gravity. The gravitational duality reveals, in turn, a wide range of new IR phenomena, including aspects of the double copy for scattering amplitudes, asymptotic symmetries and more. |
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Speaker: Marcelo DisconziTitle: General-relativistic viscous fluidsVenue: virtualGeneral Relativity Seminar Speaker: Marcelo Disconzi, Vanderbilt University Title: General-relativistic viscous fluids Abstract: The discovery of the quark-gluon plasma that forms in heavy-ion collision experiments provides a unique opportunity to study the properties of matter under extreme conditions, as the quark-gluon plasma is the hottest, smallest, and densest fluid known to humanity. Studying the quark-gluon plasma also provides a window into the earliest moments of the universe, since microseconds after the Big Bang the universe was filled with matter in the form of the quark-gluon plasma. For more than two decades, the community has intensely studied the quark-gluon plasma with the help of a rich interaction between experiments, theory, phenomenology, and numerical simulations. From these investigations, a coherent picture has emerged, indicating that the quark-gluon plasma behaves essentially like a relativistic liquid… |
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Speaker: Nikolaos AthanasiouTitle: A scale-critical trapped surface formation criterion for the Einstein-Maxwell systemVenue: CMSA Room G10General Relativity Seminar Speaker: Nikolaos Athanasiou Title: A scale-critical trapped surface formation criterion for the Einstein-Maxwell system Abstract: Few notions within the realm of mathematical physics succeed in capturing the imagination and inspiring awe as well as that of a black hole. First encountered in the Schwarzschild solution, discovered a few months after the presentation of the Field Equations of General Relativity at the Prussian Academy of Sciences, the black hole as a mathematical phenomenon accompanies and prominently features within the history of General Relativity since its inception. In this talk we will lay out a brief history of the question of dynamical black hole formation in General Relativity and discuss a result, in collaboration with Xinliang… |
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Speaker: Professor Pau FiguerasTitle: The Gregory-Laflamme instability of black strings revisitedVenue: CMSA Room G10General Relativity Seminar Title: The Gregory-Laflamme instability of black strings revisited Abstract: In this talk I will discuss our recent work that reproduces and extends the famous work of Lehner and Pretorius on the end point of the Gregory-Laflamme instability of black strings. We consider black strings of different thicknesses and our numerics allow us to get closer to the singularity than ever before. In particular, while our results support the picture of the formation of a naked singularity in finite asymptotic time, the process is more complex than previously thought. In addition, we obtain some hints about the nature of the singularity that controls the pinch off of the string. |
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Speaker: Harvey ReallTitle: The second law of black hole mechanics in effective field theoryVenue: CMSA Room G10General Relativity Seminar Speaker: Professor Harvey Reall (University of Cambridge) Title: The second law of black hole mechanics in effective field theory Abstract: I shall discuss the second law of black hole mechanics in gravitational theories with higher derivative terms in the action. Wall has described a method for defining an entropy that satisfies the second law to linear order in perturbations around a stationary black hole. I shall explain how this can be extended to define an entropy that satisfies the second law to quadratic order in perturbations, provided that one treats the higher derivative terms in the sense of effective field theory. This talk is based on work with Stefan Hollands and Aron Kovacs. Video |
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Speaker: Allen Fang, Sorbonne UniversityTitle: A new proof for the nonlinear stability of slowly-rotating Kerr-de SitterVenue: VirtualAbstract: The nonlinear stability of the slowly-rotating Kerr-de Sitter family was first proven by Hintz and Vasy in 2016 using microlocal techniques. In my talk, I will present a novel proof of the nonlinear stability of slowly-rotating Kerr-de Sitter spacetimes that avoids frequency-space techniques outside of a neighborhood of the trapped set. The proof uses vectorfield techniques to uncover a spectral gap corresponding to exponential decay at the level of the linearized equation. The exponential decay of solutions to the linearized problem is then used in a bootstrap proof to conclude nonlinear stability. |
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Speaker: Jinhua Wang, Xiamen UniversityTitle: Future stability of the $1+3$ Milne model for the Einstein-Klein-Gordon systemVenue: VirtualAbstract: We study the small perturbations of the $1+3$-dimensional Milne model for the Einstein-Klein-Gordon (EKG) system. We prove the nonlinear future stability, and show that the perturbed spacetimes are future causally geodesically complete. For the proof, we work within the constant mean curvature (CMC) gauge and focus on the $1+3$ splitting of the Bianchi-Klein-Gordon equations. Moreover, we treat the Bianchi-Klein-Gordon equations as evolution equations and establish the energy scheme in the sense that we only commute the Bianchi-Klein-Gordon equations with spatially covariant derivatives while normal derivative is not allowed. We propose some refined estimates for lapse and the hierarchies of energy estimates to close the energy argument. |
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Speaker: Chao Liu (HUST)Title: Global existence and stability of de Sitter-like solutions to the Einstein-Yang-Mills equations in spacetime dimensions n≥4Venue: virtualAbstract: In this talk, we briefly introduce our recent work on establishing the global existence and stability to the future of non-linear perturbation of de Sitter-like solutions to the Einstein-Yang-Mills system in n≥4 spacetime dimension. This generalizes Friedrich’s (1991) Einstein-Yang-Mills stability results in dimension n=4 to all higher dimensions. This is a joint work with Todd A. Oliynyk and Jinhua Wang. |