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DTSTART;TZID=America/New_York:20250204T110000
DTEND;TZID=America/New_York:20250204T120000
DTSTAMP:20260413T192242
CREATED:20240903T192049Z
LAST-MODIFIED:20250130T190257Z
UID:10003428-1738666800-1738670400@cmsa.fas.harvard.edu
SUMMARY:The mass angular momentum inequality
DESCRIPTION:General Relativity Seminar \nSpeaker: Gilbert Weinstein\, Ariel University \nTitle: The mass angular momentum inequality \nAbstract: We show that either there is a counterexample to black hole uniqueness\, in the form of a regular axisymmetric stationary vacuum spacetime with an asymptotically flat end and multiple degenerate horizons which is ‘ADM stable’\, or the following statement holds. Complete\, simply connected\, maximal initial data sets for the Einstein equations with multiple ends that are either asymptotically flat or asymptotically cylindrical\, admit an ADM mass lower bound given by the square root of total angular momentum\, under the assumption of nonnegative energy density and axisymmetry. Moreover\, equality is achieved bound only for a constant time slice of an extreme Kerr spacetime. The proof is based on a novel flow of singular harmonic maps with hyperbolic plane target\, under which the renormalized harmonic energy is monotonically nonincreasing. Relevant properties of the flow are achieved through a refined asymptotic analysis of solutions to the linearized harmonic map equations.
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar-2425/
LOCATION:Virtual
CATEGORIES:General Relativity Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-GR-Seminar-2.4.25.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20250211T110000
DTEND;TZID=America/New_York:20250211T120000
DTSTAMP:20260413T192242
CREATED:20250128T211214Z
LAST-MODIFIED:20250210T141458Z
UID:10003698-1739271600-1739275200@cmsa.fas.harvard.edu
SUMMARY:On the past maximal development of near-FLRW data for the  Einstein scalar-field Vlasov system
DESCRIPTION:General Relativity Seminar \nSpeaker: Liam Urban (University of Vienna) \n\nTitle: On the past maximal development of near-FLRW data for the Einstein scalar-field Vlasov system \nAbstract: In recent years\, the formation of Big Bang singularities has been increasingly well understood in presence of scalar-field matter\, which suppresses the geometric oscillations that one generically expects otherwise. From a cosmological perspective\, however\, one would like to understand whether this feature persists when coupled to further models that more closely resemble the matter content in our universe. \nIn this talk\, I will discuss the past nonlinear stability of FLRW solutions to the Einstein scalar-field Vlasov system in three and four spacetime dimensions without symmetry assumptions. The latter is based on joint work with David Fajman. In both works\, near-FLRW solutions are\nshown to be asymptotically velocity term dominated toward the past\,  resulting in a quiescent Big Bang singularity with stable Kretschmann scalar blow-up. The Vlasov distribution\, however\, becomes highly anisotropic towards the Big Bang singularity\, concentrating in preferred momentum directions associated with eigendirections of the shear. To ensure that the scalar field sufficiently mitigates this behaviour\, one crucially exploits a scaling hierarchy between horizontal and vertical derivatives in the expansion normalized Vlasov equation. In four\nspacetime dimensions\, this analysis is paired with a Bel-Robinson energy formalism to control the spacetime and scalar field evolution\, while one finds a significantly more direct proof in three dimensions since the spatial Riemann curvature is pure trace. \nAs a corollary\, one also obtains that the Strong Cosmic Censorship conjecture holds for four-dimensional polarized $U(1)$-symmetric solutions to the Einstein vacuum equations with spatial topology $M\times\S^1$ and isotropic quotient.
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar-21125/
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/1738856087821-8bd46bd5-9d75-4777-80dd-59b2ca5dc8d52025_1.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20250218T110000
DTEND;TZID=America/New_York:20250218T120000
DTSTAMP:20260413T192242
CREATED:20240903T191953Z
LAST-MODIFIED:20250219T144101Z
UID:10003426-1739876400-1739880000@cmsa.fas.harvard.edu
SUMMARY:General Relativity Seminar
DESCRIPTION:General Relativity Seminar \nSpeaker: Maximilian Ofner\, University of Vienna \nTitle: Stability and Instability of Relativistic Fluids in Slowly Expanding Spacetimes \nAbstract: Homogeneous and isotropic solutions to the relativistic Euler equations are known to be unstable on a Minkowski background. However\, for FLRW models with a fast expansion rate\, relativistic fluids stabilize. This scenario suggests a transition between stable and unstable behavior\, somewhere along a family of spacetimes parametrized by their expansion rate. In this talk we will discuss this phase transition for various equations of state\, focusing on the regime of linear and decelerated expansion. This is based on recent analytical results\, complemented by numerical analysis.
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar-21825/
LOCATION:Virtual
CATEGORIES:General Relativity Seminar
ATTACH;FMTTYPE=image/png:https://cmsa.fas.harvard.edu/media/CMSA-GR-Seminar-2.18.25.png
END:VEVENT
BEGIN:VEVENT
DTSTART;TZID=America/New_York:20250225T110000
DTEND;TZID=America/New_York:20250225T120000
DTSTAMP:20260413T192242
CREATED:20240903T183821Z
LAST-MODIFIED:20250228T212719Z
UID:10003420-1740481200-1740484800@cmsa.fas.harvard.edu
SUMMARY:BKL bounces outside homogeneity
DESCRIPTION:General Relativity Seminar \nSpeaker: Warren Li ( Princeton University) \nTitle: BKL bounces outside homogeneity \nAbstract: In work spanning the late 20th century\, physicists Belinski\, Khalatnikov and Lifshitz (BKL) proposed a general ansatz for solutions to the Einstein (vacuum) equations near singularities. They suggest that the spacetime dynamics at different spatial points on the singularity decouple and are well-approximated by a system of autonomous nonlinear ODEs\, whose orbits are governed by a chaotic cascade of “BKL bounces”. In this talk\, we present recent work verifying BKL’s heuristics in a large class of symmetric\, but spatially inhomogeneous\, spacetimes. In particular\, we prove decoupling even in the presence of (up to one) BKL bounce. The proof uses nonlinear ODE analysis coupled to hyperbolic energy estimates\, and one hopes our methods may be applied more generally.
URL:https://cmsa.fas.harvard.edu/event/general-relativity-seminar-22525/
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/1740157873632-2128c0f1-4416-42e5-a58b-0475ecffb3852025-1_1.png
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