Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session Y11: Analytical Calculations and Approximations in General Relativity 
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Sponsoring Units: DGRAV Chair: Steve Carlip, University of California, Davis Room: Sheraton Governor's Square 17 
Tuesday, April 16, 2019 1:30PM  1:42PM 
Y11.00001: Coulombic contribution to angular momentum flux in general relativity Beatrice Bonga, Eric Poisson Angular momentum flux in electromagnetism cannot be expressed entirely in terms of the field's radiative degrees of freedom. Its expression also involves Coulombic parts of the field, in the form of a charge aspect $q(\theta,\phi)$. Guided by the strong analogy between radiative processes in electromagnetism and gravitation, one might expect that the angular momentum flux in general relativity also involves 'Coulombic pieces' that may have been missed by specializing the flux to periodic sources at rest with respect to the frame in which the flux is evaluated. To test this, we bring together the LandauLifshitz formalism, which provides specific definitions for angular momentum and its associated flux, and the Bondi formalism, which provides a systematic expansion of the metric of any asymptotically flat spacetime in inverse powers of the distance away from the matter distribution. We obtain a new expression for the flux of angular momentum, which is not restricted to sources at rest nor to periodic sources. This new expression is equivalent to the standard formula when these restrictions are put in place. Contrary to expectations based on the analogy between electromagnetism and gravitation, no Coulombic information appears in the flux of angular momentum in general relativity. 
Tuesday, April 16, 2019 1:42PM  1:54PM 
Y11.00002: Nonaxial angular momentum fluxes and black hole perturbation theory Karna Ashwin Morey, Scott A Hughes Motivated largely by the need to develop accurate models for extreme mass ratio inspirals that will be measured by the planned LISA mission, there has been great progress in recent years modeling binaries in which one member is far more massive than the other. In the adiabatic limit, the action of the dissipative selfforce which drives the evolution of such a system is equivalent to using simple ``fluxbalancing’’ results, describing how a geodesic’s energy, axial angular momentum, and Carter constant change due to gravitational wave backreaction. A clear calculation of the nonaxial components of angular momentum carried by gravitational waves has recently appeared in the literature. We demonstrate that, at least for a small body orbiting a Schwarzschild black hole, this calculation takes a particularly simple form by reorganizing the terms into the action of the spinweighted spherical harmonic raising and lowering operators acting on curvature scalars. We apply this result to fluxes computed using black hole perturbation theory. We then discuss the groundwork for extending these calculations first to slowly rotating black holes and then to general Kerr holes, as well as potential applications of this framework to other problems in black hole perturbation theory. 

Y11.00003: ABSTRACT WITHDRAWN

Tuesday, April 16, 2019 2:06PM  2:18PM 
Y11.00004: Horizon instability of the extremal BTZ black hole Samuel Gralla, Arun Ravishankar, Peter Zimmerman Extremal black holes exhibit a universal horizon instability (Aretakis instability). We study the simplest possible system, a scalar field perturbing the BTZ black hole, and obtain the retarded Green function in closed form, allowing us to unite different methods used previously for special cases. We hope this insight will be useful in unravelling the astrophysical and holographic implications of this universal instability. 

Y11.00005: ABSTRACT WITHDRAWN

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