Bulletin of the American Physical Society
APS April Meeting 2019
Volume 64, Number 3
Saturday–Tuesday, April 13–16, 2019; Denver, Colorado
Session R15: Gravitational Waves and Strongfield Dynamics 
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Sponsoring Units: DGRAV Chair: Kent Yagi, University of Virginia Room: Sheraton Plaza Court 4 
Monday, April 15, 2019 1:30PM  1:42PM 
R15.00001: Testing for Lorentz Invariance Violation through Birefringence Effects of Gravitational Waves Kellie AultO'Neal, Quentin G Bailey General Relativity and the Standard Model are two experimentally supported theories, yet a consistent unified quantum theory of gravity at the Planck scale is still to be found. Built into these theories are CPT and Lorentz Symmetries; attempts to unify the two theories may involve breaking these symmetries. Using the effective theory framework, the Standard Model Extension (SME) lays out all possible background field tensors that can couple to known fields. In this way, one can test for the generic symmetric breaking of existing fields. In particular, we discuss using LIGOVIRGO gravitational wave data as a means of testing Lorentz symmetry. A possible observable effect is birefringence, where there would be a small shift in the arrival times between the two gravitational wave polarizations from a distant source to detectors. 
Monday, April 15, 2019 1:42PM  1:54PM 
R15.00002: Validation of the nonlinearities in general relativity from a population of gravitational wave observations CarlJohan O Haster The nonlinear terms in the expressions for the timeevolving phase of gravitational wave emission from a compact object binary can be formulated through both sourcespecific and populationspanning parameters. 
Monday, April 15, 2019 1:54PM  2:06PM 
R15.00003: Probing Screening and the Graviton Mass with Gravitational Waves Scott E Perkins, Nicolás Yunes Gravitational waves have been used previously to constrain many fundamental quantities in physics, including the mass of the graviton. However, these bounds have neglected the effect of screening, which is typically present in modified theories that predict a nonzero graviton mass. In this talk, I will first show how a previously derived correction to the propagation of gravitational waves sourced by a massive graviton is affected by screening processes. After that, I will present the numerical results we have obtained that predict how well future gravitational wave detectors can constrain the screened graviton mass in a modelindependent interpretation. As screening effects and modifications to General Relativity are competing effects, this will define a degenerate bound on the screening radius and the graviton mass. 
Monday, April 15, 2019 2:06PM  2:18PM 
R15.00004: Dynamics of Collapsing Spherically Symmetric Massive Scalar Domain Wall Soumyajit Bose, David F Chernoff The collapse of a spherically symmetric thick domain wall, modeled by a scalar field, is investigated. The collapse happens in the presence of a potential with two minima. The dependence of the mass spectrum of the final Black Hole state on various parameters of the field is studied using numerical relativity techniques, in particular in a BaumgarteShapiroShibataNakamura(BSSN) setup. Further, qualitative and quantitative parallels are drawn between the above setup, and different existing thin shell models. 
Monday, April 15, 2019 2:18PM  2:30PM 
R15.00005: Beyond Forcefree Electrodynamics: Effective Field Theory and Bosonization Samuel Elliot Gralla Forcefree electrodynamics (FFE) is a closed set of equations for the electromagnetic field of a magnetically dominated plasma. There are strong arguments for the existence of forcefree plasmas near pulsars and active black holes, but FFE alone cannot account for the observational signatures, such as coherent radio emission and relativistic jets and winds. I will describe two approaches to going beyond FFE: effective field theory of a cold string plasma (w/ N. Iqbal) and bosonization on the lowest Landau level. 
Monday, April 15, 2019 2:30PM  2:42PM 
R15.00006: Polarization Whorls from HighSpin Black Holes Delilah E Gates, Daniel Kapec, Alexandru Lupsasca, Yichen Shi, Andrew Eben Strominger The Event Horizon Telescope (EHT) is expected to soon produce polarimetric images 
Monday, April 15, 2019 2:42PM  2:54PM 
R15.00007: Small nonspherical perturbations of the Choptuik spacetime decay, but large ones may grow Thomas W Baumgarte The Choptuik spacetime is the discretely selfsimilar, spherically symmetric critical solution that emerges at the threshold of blackhole formation in the gravitational collapse of a massless scalar field. Studying linear perturbations of this solution, MartinGarcia and Gundlach found that all nonspherical perturbations decay. In an apparent contradiction, Choptuik et.al. found that some nonspherical deformations grew in their numerical simulations, ultimately leading to a bifurcation of the critical solution. I will report on new numerical simulations of the critical collapse of scalar fields in the absence of spherical symmetry. For small deviations from spherical symmetry, the deformations perform damped oscillations that are consistent with the findings of MartinGarcia and Gundlach. For larger deviations, however, the deformations grow and form new centers of oscillations, consistent with the bifurcations observed by Choptuik et.al.. I speculate that this qualitative change in behavior is caused by nonlinear effects that lead to shifts in the parameters describing the critical solution and its deformations. 
Monday, April 15, 2019 2:54PM  3:06PM 
R15.00008: Parametrising the black hole quasinormal ringdown Ryan McManus, Emanuele Berti, Vitor Cardoso, Andrea Maselli, Masashi Kimura, Caio Macedo It is well known that black hole solutions in general relativity are surprisingly simple as shown by the nohair theorems. Even more surprising is that for many modified gravity theories, nohair theorems also exist. However, gravitational waves emitted during a black hole binary merger allow for discrimination between various gravity theories as the waves evolve according to different equations of motion. Of particular interest is the ringdown signal postmerger, described by a discrete spectrum of quasinormal modes. These spectra are fingerprints of the underlying gravity theory and so provide a simple yet powerful test of GR. As with all tests, the predictions made by other gravity theories need to be computed, but this is a highly laborious undertaking given the vast number of modified gravity theories that exist. We present recent work parametrising the expected deviations from the GR frequencies in a theoryindependent manner. 
Monday, April 15, 2019 3:06PM  3:18PM 
R15.00009: The outflying singularity inside fast spinning black holes Lior M Burko, Gaurav Khanna Marolf and Ori proposed a shock wave singularity along the outgoing segment of the inner horizon (OIH) of black holes. Previous evidence stems mostly from spherical charged toy models with scalar fields or scalar fields in addition to null fluids, or from a scalar field model for a rotating black hole (but with initial data that are not well motivated astrophysically, specifically external perturbations). We consider linearized perturbations of fast rotating Kerr black holes, for either scalar field or vacuum, gravitational perturbations. The perturbation fields are the fields that result from the collapse of an isolated black hole (“Price tails”). We show the occurrence of a MarolfOri like singularity at the OIH (“outflying singularity”) as experienced by either null or timelike observers. This singularity joins a null, weak singularity (“mass inflation”, “infalling”) at the ingoing leg. We then study in detail the quantitative features of the outflying singularity, specifically the shock sharpening effect of the scalar field for scalar field perturbations, and the Weyl scalars ψ_{0} and ψ_{4 }(scaled appropriately by the horizon function Δ), and the Kretschmann curvature scalar K for gravitational perturbations, and show that in all cases its rate agrees with expectations. .

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