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BEGIN:VEVENT
DTSTART;TZID=America/New_York:20240513T110000
DTEND;TZID=America/New_York:20240513T120000
DTSTAMP:20260505T171930
CREATED:20240411T181646Z
LAST-MODIFIED:20240514T142424Z
UID:10003354-1715598000-1715601600@cmsa.fas.harvard.edu
SUMMARY:An analogue of non-interacting quantum field theory in Riemannian signature
DESCRIPTION:General Relativity Seminar \nSpeaker: Mikhail Molodyk\, Stanford \nTitle: An analogue of non-interacting quantum field theory in Riemannian signature \nAbstract: Recent advances using microlocal tools have led to constructions\, for wave operators on various classes of spacetimes\, of four distinguished Fredholm inverses which have the singular behavior required of retarded\, advanced\, Feynman\, and anti-Feynman propagators in QFT. Vasy and Wrochna have used these to define a QFT on asymptotically Minkowski spacetimes\, for which they construct Hadamard states described by asymptotic data at infinity. I will describe an analogue of this construction on Riemannian manifolds with two asymptotically conic ends\, defining quantum fields satisfying the Helmholtz equation and using scattering data to construct states satisfying a wavefront mapping-property version of the Hadamard condition. The absence of a spacetime interpretation lends itself to a sharper focus on the theory’s analytic structure\, from whose perspective the Feynman propagators are no less natural than the advanced/retarded ones. I will also highlight some differences between Feynman propagators defined as distinguished inverses and as time-ordered expectations. Based on joint work with András Vasy.
URL:https://cmsa.fas.harvard.edu/event/general-relativity-51324/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:General Relativity Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-GR-Seminar-05.13.2024.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20240507T140000
DTEND;TZID=America/New_York:20240507T150000
DTSTAMP:20260505T171930
CREATED:20240411T181320Z
LAST-MODIFIED:20240819T151524Z
UID:10000835-1715090400-1715094000@cmsa.fas.harvard.edu
SUMMARY:Real-time observables in horizon thermodynamics
DESCRIPTION:General Relativity Seminar \nSpeaker: Albert Law\, Stanford \nTitle: Real-time observables in horizon thermodynamics \nAbstract: Euclidean black hole 1-loop determinants have recently been shown to compute a renormalized thermal canonical partition function for free fields in Lorentzian signature. A key ingredient is a ‘quasinormal mode (QNM) character’\, whose Fourier transform equals the renormalized spectral density of the single-particle Hamiltonian. Using a static patch in de Sitter space as an example\, in this talk\, I will offer new perspectives on the QNM character\, including its connection with the local density of states for the single-particle quantum mechanical problem associated with the Klein-Gordon equation\, and its direct relationships with (thermal) correlators of the free fields. I will discuss how these considerations might point toward a generalization to interacting theories.
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar-5724/
LOCATION:Virtual
CATEGORIES:General Relativity Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-GR-Seminar-05.7.2024.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20240423T100000
DTEND;TZID=America/New_York:20240423T110000
DTSTAMP:20260505T171930
CREATED:20240415T162430Z
LAST-MODIFIED:20240422T154105Z
UID:10000833-1713866400-1713870000@cmsa.fas.harvard.edu
SUMMARY:Quantum Energy Inequalities
DESCRIPTION:General Relativity Seminar \nSpeaker: Chris Fewster\, York University \nTitle: Quantum Energy Inequalities \nAbstract: Many theorems of mathematical relativity\, including singularity and positive mass theorems\, include the classical energy conditions among their hypotheses. However\, matter described by quantum field theory can violate the classical energy conditions and indeed there is no lower bound to the energy density at a given point as the quantum state is varied. Do the classical theorems apply to quantised matter? \nIn this talk I discuss Quantum Energy Inequalities\, lower bounds on averages of the energy density along timelike curves or over spacetime regions\, that have been proved in QFT and are the remnants of the classical energy conditions after quantisation. I will also discuss some of their consequences.
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar_42324/
LOCATION:Virtual
CATEGORIES:General Relativity Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20240416T110000
DTEND;TZID=America/New_York:20240416T120000
DTSTAMP:20260505T171930
CREATED:20240409T163938Z
LAST-MODIFIED:20240502T195940Z
UID:10000832-1713265200-1713268800@cmsa.fas.harvard.edu
SUMMARY:New Well-Posed Boundary Conditions for Semi-Classical Euclidean Gravity
DESCRIPTION:General Relativity Seminar \nSpeaker: Xiaoyi Liu\, UCSB \nTitle: New Well-Posed Boundary Conditions for Semi-Classical Euclidean Gravity \nAbstract: We consider four-dimensional Euclidean gravity in a finite cavity.  We point out that there exists a one-parameter family of boundary conditions\, parameterized by a real constant\, where a suitably Weyl-rescaled boundary metric is fixed\, and all give a well-posed elliptic system\, as opposed to the Dirichlet boundary condition. Focussing on static Euclidean solutions\, we derive a thermodynamic first law. Restricting to a spherical spatial boundary\, the infillings are flat space or the Schwarzschild solution and have similar thermodynamics to the Dirichlet case. We study the stability behavior of several geometries under these boundary conditions in both Euclidean and Lorentzian signatures and find two puzzles.
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar_41624/
LOCATION:Virtual
CATEGORIES:General Relativity Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-GR-Seminar-04.16.2024.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20240402T110000
DTEND;TZID=America/New_York:20240402T120000
DTSTAMP:20260505T171930
CREATED:20240325T132956Z
LAST-MODIFIED:20240325T150323Z
UID:10000830-1712055600-1712059200@cmsa.fas.harvard.edu
SUMMARY:Linearised Second Law for Higher Curvature Gravity and Non-Minimally Coupled Vector Fields
DESCRIPTION:General Relativity Seminar \nSpeaker: Zihan Yan\, Cambridge University \n\n\n\nTitle: Linearised Second Law for Higher Curvature Gravity and Non-Minimally Coupled Vector Fields \n\n\n\nAbstract: Expanding the work of arXiv:1504.08040\, we show that black holes obey a second law for linear perturbations to bifurcate Killing horizons\, in any covariant higher curvature gravity coupled to scalar and vector fields. The vector fields do not need to be gauged\, and (like the scalars) can have arbitrary non-minimal couplings to the metric. The increasing entropy has a natural expression in covariant phase space language\, which makes it manifestly invariant under JKM ambiguities. An explicit entropy formula is given for f(Riemann) gravity coupled to vectors\, where at most one derivative acts on each vector. Besides the previously known curvature terms\, there are three extra terms involving differentiating the Lagrangian by the symmetric vector derivative (which therefore vanish for gauge fields).
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar-3/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:General Relativity Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-GR-Seminar-04.02.2024.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20240319T103000
DTEND;TZID=America/New_York:20240319T113000
DTSTAMP:20260505T171930
CREATED:20240318T134919Z
LAST-MODIFIED:20240318T135543Z
UID:10000828-1710844200-1710847800@cmsa.fas.harvard.edu
SUMMARY:Scattering Rigidity Problem
DESCRIPTION:General Relativity Seminar \nSpeaker: Jin Jia\, Hunan University \nTitle: Scattering Rigidity Problem \nAbstract: If the asymptotic behavior of a solution to a nonlinear equation is the same as that of a solution to its linearized equation\, it is called a scattering solution. Scattering phenomena are widely observed near steady-state solutions of various mathematical physics equations\, such as water wave equations\, Einstein equations\, MHD equations\, and Vlasov-Poisson equations. This report takes these equations as examples to provide the definition of scattering operator and its relation to radiation fields. It explains the concepts of scattering rigidity problem and scattering completeness problem\, and introduces the latest discoveries of the speaker in the general solution approach to scattering rigidity problem.
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar-31924/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:General Relativity Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20240305T110000
DTEND;TZID=America/New_York:20240305T120000
DTSTAMP:20260505T171930
CREATED:20240229T165205Z
LAST-MODIFIED:20240813T154631Z
UID:10000827-1709636400-1709640000@cmsa.fas.harvard.edu
SUMMARY:High order WENO finite difference scheme  for Einstein-Yang-Mills equations
DESCRIPTION:General Relativity Seminar \nSpeaker: Yuewen Chen\, Tsinghua University \nTitle: High order WENO finite difference scheme  for Einstein-Yang-Mills equations \nAbstract: In this talk\, we will show the convergence analysis of the first-order finite difference scheme for static spherically symmetric $SU(2)$ Einstein-Yang-Mills (EYM) equations. We also construct a new WENO scheme for EYM.
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar-3524/
LOCATION:Virtual
CATEGORIES:General Relativity Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-GR-Seminar-03.05.2024.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20240227T110000
DTEND;TZID=America/New_York:20240227T120000
DTSTAMP:20260505T171930
CREATED:20240226T152845Z
LAST-MODIFIED:20240227T193918Z
UID:10000826-1709031600-1709035200@cmsa.fas.harvard.edu
SUMMARY:On Axially Symmetric Perturbations of Kerr Black Hole Spacetimes
DESCRIPTION:General Relativity Seminar \nSpeaker: Nishanth Gudapati\, Clark University \nTitle: On Axially Symmetric Perturbations of Kerr Black Hole Spacetimes \nAbstract: The Kerr black hole stability problem is an important open problem in general relativity. In this talk\, I will focus on the role of energy methods in the axisymmetric stability of Kerr black hole spacetimes. In particular\, I will discuss the construction and the application of a positive Hamiltonian energy for axially symmetric Maxwell and Einstein perturbations of sub-extremal Kerr black hole spacetimes.
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar-22724/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:General Relativity Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-GR-Seminar-02.27.2024.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20240220T093000
DTEND;TZID=America/New_York:20240220T103000
DTSTAMP:20260505T171930
CREATED:20240219T195817Z
LAST-MODIFIED:20240219T195829Z
UID:10000825-1708421400-1708425000@cmsa.fas.harvard.edu
SUMMARY:Asymptotic decay for defocusing semilinear wave equations on Schwarzschild spacetimes
DESCRIPTION:General Relativity Seminar \nSpeaker: He Mei\, Shenzhen University \nTitle: Asymptotic decay for defocusing semilinear wave equations on Schwarzschild spacetimes \nAbstract: In this talk\, I will present a work on the long time dynamics of solutions to the defocusing semilinear wave equations on the Schwarzschild black hole spacetimes. For sufficiently smooth and localized initial data\, we show that the solution decays in the domain of outer communication. The proof relies on a vector field method of Dafermos-Rodnianski together with Strichartz estimates for linear waves by Marzuola-Metcalfe-Tataru-Tohaneanu.
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar-22024/
LOCATION:Virtual
CATEGORIES:General Relativity Seminar
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20240213T110000
DTEND;TZID=America/New_York:20240213T110000
DTSTAMP:20260505T171930
CREATED:20240212T161202Z
LAST-MODIFIED:20240212T181141Z
UID:10000824-1707822000-1707822000@cmsa.fas.harvard.edu
SUMMARY:Characteristic Initial Value Problem for the 3D Compressible Euler Equations
DESCRIPTION:General Relativity Seminar \nSpeaker: Sifan Yu\, NUS \nTitle: Characteristic Initial Value Problem for the 3D Compressible Euler Equations \nAbstract: We present the first result for the characteristic initial value problem of the compressible Euler equations in three space dimensions without any symmetry assumption. We allow presence of vorticity and consider any equation of state. Compared to the standard Cauchy problem\, where initial data can be freely prescribed on a constant-time hypersurface\, we formulate the problem by distinguishing between the “free-component” and the “constrained-component” of the initial data. The latter is to be solved by the “free-component” utilizing the properties of the compressible Euler equations on the initial null hypersurfaces. Then\, we establish a priori estimates\, followed by a local well-posedness and a continuation criterion argument. Moreover\, we prove a regularity theory in Sobolev norms. Our analysis critically relies on the vectorfield method due to the nature of the problem. This is a joint work with Jared Speck.
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar-21324/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:General Relativity Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-GR-Seminar-02.13.2024.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20240206T100000
DTEND;TZID=America/New_York:20240206T110000
DTSTAMP:20260505T171930
CREATED:20240202T170516Z
LAST-MODIFIED:20240209T200944Z
UID:10000823-1707213600-1707217200@cmsa.fas.harvard.edu
SUMMARY:Noncompact n-dimensional Einstein spaces as attractors for the Einstein flow
DESCRIPTION:General Relativity Seminar \nSpeaker: Jinhua Wang\, Xiamen University \nTitle: Noncompact n-dimensional Einstein spaces as attractors for the Einstein flow \nAbstract: We prove that along with the Einstein flow\, any small perturbations of an $n$($n\geq4$)-dimensional\, non-compact negative Einstein space with some “non-positive Weyl tensor” lead to a unique and global solution\, and the solution will be attracted to a noncompact Einstein space that is close to the background one. The $n=3$ case has been addressed by Wang-Yuan\, while in dimension $n\geq 4$\, as we know\, negative Einstein metrics in general have non-trivial moduli spaces. This fact is reflected on the structure of Einstein equations\, which further indicates no decay for the spatial Weyl tensor. Furthermore\, it is suggested in the proof that the mechanic preventing the metric from flowing back to the original Einstein metric lies in the non-decaying character of spatial Weyl tensor. In contrary to the compact case considered in Andersson-Moncrief\, our proof is independent of the theory of infinitesimal Einstein deformations. Instead\, we take advantage of the inherent geometric structures of Einstein equations and develop an approach of energy estimates for a hyperbolic system of Maxwell type. \nReferences – arXiv: 2209.15244\, 2309.15152\, 2311.00868
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar-2624/
LOCATION:Virtual
CATEGORIES:General Relativity Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-GR-Seminar-02.06.2024.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20240130T110000
DTEND;TZID=America/New_York:20240130T120000
DTSTAMP:20260505T171930
CREATED:20240126T184234Z
LAST-MODIFIED:20240813T154857Z
UID:10000822-1706612400-1706616000@cmsa.fas.harvard.edu
SUMMARY:A quasi-local mass in general relativity
DESCRIPTION:General Relativity Seminar \nSpeaker: Aghil Alaee\, Clark University \nTitle: A quasi-local mass in general relativity \nAbstract: In this talk\, we define a new gauge-independent quasi-local mass and energy with respect to the Minkowski spacetime. In contrast to other quasi-local masses\, this new quasi-local mass/energy has a quasi-local proof of positivity. This positivity property is for spacelike surfaces with any topology.  Moreover\, we show that it has desired asymptotic behaviors at null and spatial infinity of asymptotically flat spacetimes. Rigidity is also established in that vanishing energy implies that the 2-surface arises from an embedding into Minkowski space\, and conversely\, the mass vanishes for any such surface. This is joint work with M. Khuri and S.T. Yau. \n 
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar-13024/
LOCATION:CMSA Room G10\, CMSA\, 20 Garden Street\, Cambridge\, MA\, 02138\, United States
CATEGORIES:General Relativity Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-GR-Seminar-01.30.2024.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20230926T110000
DTEND;TZID=America/New_York:20230926T120000
DTSTAMP:20260505T171930
CREATED:20240223T104632Z
LAST-MODIFIED:20240813T160129Z
UID:10002850-1695726000-1695729600@cmsa.fas.harvard.edu
SUMMARY:Geometry at Strong coupling for amplitudes/Wilson loops
DESCRIPTION:General Relativity Seminar \nSpeaker: Lionel Mason (Oxford) \nTitle: Geometry at Strong coupling for amplitudes/Wilson loops \nAbstract: The amplitude/Wilson loop correspondence identifies planar N=4 super-Yang-Mills amplitudes with certain null polygonal Wilson loops at all the values of the coupling. At strong coupling this equates the amplitude/Wilson loop computed by Alday & Maldacena in terms of the area of a minimal surface in AdS_5. To do so they developed a `Y-system’ for computing the amplitude. This talk re-interprets their construction as providing the underlying twistor space for a hyperKahler structure on the corresponding space of kinematic data. In particular\, the area is given by a Kahler scalar for the pseudo-hyperkahler structure and satisfies a version of the Plebanski equations\, a well-known completely integrable system. This geometry encodes the properties of the space of kinematic data on which the amplitude depends as a cluster variety tying into its positive geometry and cluster variety structure. Similar constructures are possible for other cluster varieties corresponding to form factors and beyond.
URL:https://cmsa.fas.harvard.edu/event/gr_92623/
CATEGORIES:General Relativity Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-GR-Seminar-09.26.23.png
END:VEVENT
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