Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session R13: Mathematical Aspects of General Relativity |
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Sponsoring Units: DGRAV Chair: Deborah Konkowski, U.S. Naval Academy Room: A224-225 |
Monday, April 16, 2018 10:45AM - 10:57AM |
R13.00001: Conservation of asymptotic charges from past to future null infinity Kartik Prabhu We show that asymptotic symmetries and charges on past null infinity can be matched to those on future null infinity using the Ashtekar-Hansen structure of spatial infinity. This provides a conservation law for asymptotic charges from past to future null infinity in a general class of spacetimes. We focus on electromagnetic fields and comment on the generalization to supertranslations in General Relativity. We also comment on the extension to the full BMS group of symmetries. [Preview Abstract] |
Monday, April 16, 2018 10:57AM - 11:09AM |
R13.00002: Symmetries and Charges of General Relativity at Null Boundaries Venkatesa Chandrasekaran, Kartik Prabhu, Eanna Flanagan Motivated by the recent suggestion that supertranslations and the associated "soft hair" play an important role in the black hole information problem, we study general relativity at a null boundary using the covariant phase space formalism. We describe the universal structure induced on null boundaries and find the algebra of symmetries preserving this universal structure. We discuss the similarities and differences with the BMS algebra at null infinity. Using the general prescription of Wald and Zoupas, we derive the conserved charges and fluxes of this symmetry algebra. Our analysis is covariant, holds in all dimensions, and applies to general non-stationary null surfaces. [Preview Abstract] |
Monday, April 16, 2018 11:09AM - 11:21AM |
R13.00003: Gravitational wave memory observables Alexander Grant, Eanna Flanagan, Abraham Harte, David Nichols Gravitational wave memory is characterized by the permanent relative displacement of a pair of initially comoving test particles caused by the passage of a burst of gravitational waves. We describe a number of generalizations of this effect. For initially comoving, spinless test particles these effects were identified in previous work and include a net relative boost, a net relative rotation of their inertial frames, and a difference in elapsed proper time. For particles with an initial relative velocity, these observables can be used to measure the spin memory effect of Pasterski, Strominger and Zhiboedov, while for particles with spin, there are additional, qualitatively different observables which we describe. [Preview Abstract] |
Monday, April 16, 2018 11:21AM - 11:33AM |
R13.00004: The Memory Effect of Particle Scattering in Odd Spacetime Dimensions Gautam Satishchandran, Robert Wald The gravitational memory effect is the permanent displacement of test particles due to the passage of gravitational waves. We investigate the memory effect for linearized perturbations off of Minkowski space in odd spacetime dimension $d$ by examining the effects of gravitational radiation from point particle scattering. We find that there is no gravitational memory effect in all odd dimensions. Our results are further elucidated by analyzing the memory effect for any slowly moving source of compact spatial support in odd dimensions. [Preview Abstract] |
Monday, April 16, 2018 11:33AM - 11:45AM |
R13.00005: A geometric framework for cosmological spacetimes BĂ©atrice Bonga, Kartik Prabhu Null infinity in asymptotically flat spacetimes posses a rich mathematical structure; including the BMS group and the Bondi news tensor that allow one to study gravitational radiation rigorously. However, FLRW spacetimes are not asymptotically flat because their stress-energy tensor does not decay sufficiently fast and in fact diverges at null infinity. We define a large class of spacetimes whose stress-energy tensor have a singular part at null infinity that is universal. This class includes matter- and radiation-dominated FLRW spacetimes. Interestingly, for this larger class of spacetimes, the BMS algebra naturally emerges as the asymptotic symmetry. Future applications include studying the cosmological memory effect and asymptotic charges in this framework. [Preview Abstract] |
Monday, April 16, 2018 11:45AM - 11:57AM |
R13.00006: Systematics of gravitational radiation for asymptotically de Sitter spacetimes Sina Bahrami For asymptotically flat spacetimes, the Bondi-Sachs formalism provides a comprehensive description of what the observers measure at Scri. In the case of isolated binary systems, various quantities such as the fluxes of radiated gravitational energy and angular momentum can be computed using a well defined prescription. The success of this formalism hinges on the asymptotic symmetry structure that is unique to ``null'' Scri. For the case of spacelike Scri, as in asymptotically de Sitter spacetimes, no such symmetry structure has been available. In this talk I will explain some recent progress that has been made in this direction. This is work in progress in collaboration with Abhay Ashtekar and Jerzy Lewandowski. [Preview Abstract] |
Monday, April 16, 2018 11:57AM - 12:09PM |
R13.00007: Black hole scalar charge from a horizon integral in Einstein-dilaton-Gauss-Bonnet gravity Leo Stein In beyond-GR theories with a scalar field, a black hole's scalar charge is a crucial quantity for testing the theory. The scalar charge---given by an integral at spatial infinity---controls the dynamics and gravitational radiation of black hole--compact object binaries. Extracting this scalar charge would seem to require solving the field equations for a black hole spacetime. In this talk I will show that in the special case of Einstein-dilaton-Gauss-Bonnet theory, the scalar charge can instead be extracted from a horizon integral. This relationship between an integral at infinity and one on the horizon is reminiscent of mass and spin integrals in GR. [Preview Abstract] |
Monday, April 16, 2018 12:09PM - 12:21PM |
R13.00008: Fractal Dimension of Turbulent Black Holes John Ryan Westernacher-Schneider We resolve a recent claim that turbulent black holes in anti-de Sitter space have event horizons with a fractal dimension greater than 3. By constructing such event horizons using turbulent fluid simulations and the fluid-gravity duality, we measure the fractal dimension of the horizon to be $\approx 2.6$. There is mounting evidence that astrophysical black holes can become turbulent, so a covariant formulation of the fractal dimension will be useful for characterizing their states. [Preview Abstract] |
Monday, April 16, 2018 12:21PM - 12:33PM |
R13.00009: Critical Collapse in the Absence of Spherical Symmetry Thomas Baumgarte Critical phenomena in gravitational collapse refer to the appearance of universal scaling laws and a critical self-similar solution close to the threshold of black-hole formation. The seminal discovery of these phenomena by Matt Choptuik about 25 years ago triggered a large body of literature on the subject. Most of these studies, however, have assumed spherical symmetry. In this talk I will review some recent results on critical phenomena in the absence of spherical symmetry, focussing on the stability of the critical self-similar solution to aspherical modes. [Preview Abstract] |
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