Bulletin of the American Physical Society
APS April Meeting 2023
Volume 68, Number 6
Minneapolis, Minnesota (Apr 15-18)
Virtual (Apr 24-26); Time Zone: Central Time
Session Q09: Numerical Simulations III |
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Sponsoring Units: DGRAV Chair: Zachariah Etienne, University of Idaho Room: Conrad B/C - 2nd Floor |
Monday, April 17, 2023 3:45PM - 3:57PM |
Q09.00001: Critical Collapse of Gravitational Waves Thomas W Baumgarte Critical phenomena in gravitational collapse refer to self-similarity, universality, and scaling close to the onset of black-hole formation. While these phenomena are quite well understood in the context of spherical symmetry, many of their aspects remain enigmatic for the collapse of vacuum gravitational waves. I will review recent simulations of this collapse and will suggest that, while the assumption of universality does not seem to apply in the absence of spherical symmetry, there do exist families of initial data for which the threshold solution displays an at least approximate discrete self-similarity. |
Monday, April 17, 2023 3:57PM - 4:09PM |
Q09.00002: Progress in GRMHD simulations with SpECTRE Yoonsoo Kim, Nils Deppe, William T Throwe, Nils L Vu, Lawrence E Kidder, Elias R Most, Mark A Scheel, Saul A Teukolsky We present recent improvements in general relativistic hydrodynamics simulations with the open source numerical relativity code SpECTRE. Major updates include support for tabulated equations of states, implementation of higher-order and positivity-preserving adaptive order finite difference schemes in our discontinuous Galerkin-finite difference (DG-FD) hybrid solver, and integrating the DG-FD hybrid solver with spacetime evolution for fully general relativistic simulations. As a benchmark, we show a few recent tests including long-term (>100ms) stable simulations of isolated neutron star with strong magnetic field. |
Monday, April 17, 2023 4:09PM - 4:21PM |
Q09.00003: Exploring the Equation of State and Properties of Neutron Stars in f(R) Gravity Josef Zimmerman, Carolyn Raithel, Frans Pretorius In addition to a dependence on the Equation of State (EoS) of supranuclear matter, the structure and properties of Neutron Stars (NSs) are sensitive to any modification to strong-field gravity in beyond-GR theories. We computationally explore the relationship between the EoS, theory of gravity, and NS properties by simulating a large variety of NSs. By solving the analogue of the Tolman–Oppenheimer–Volkoff (TOV) equations in f(R) gravity, we obtain the mass-radius relationship of a NS described by any given EoS. In order to search a wide combination of models of gravity and EoSs, we adopt a parameterized f(R) = R + αR2 theory and a piecewise-polytropic EoS, which we show is a representative sample of possible EoSs. We developed a GPU-accelerated f(R) TOV solving code in order to rapidly and eciently explore a large parameter space of EoSs and the value of α. We explore correlations between the EoS, α, and the mass-radius relationship, including the prospect for constraints of the EoS and α based on direct observations of NSs and implications for the maximum possible mass of a NS. |
Monday, April 17, 2023 4:21PM - 4:33PM |
Q09.00004: Hyperbolic encounters of binary black holes in scalar Gauss-Bonnet gravity Frederick C Pardoe, Helvi Witek In this talk, I will present results of simulations of hyperbolic encounters of equal-mass, non-spinning black holes sourcing the scalar field in scalar Gauss-Bonnet gravity. Working at the decoupling limit, the background spacetime represents the evolution of black hole binaries in General Relativity. Depending on the impact parameter, the black holes scatter, merge or exhibit zoom-whirl orbits. I will also discuss the evolution of the Gauss-Bonnet scalar field determined by the different binary evolutions in the background and present the scalar energy flux. |
Monday, April 17, 2023 4:33PM - 4:45PM |
Q09.00005: Black Hole simulations in axi-dilaton gravity Alexandru Dima, Chloe Richards, Helvi Witek Effective field theories of gravity featuring a scalar field coupled to quadratic curvature invariants are known to predict black holes with scalar hair. The phenomenology of hairy black holes has been studied extensively in the past, focusing either on Einstein-scalar-Gauss-Bonnet or dynamical Chern-Simons gravity. Both these models can be regarded as special cases of axi-dilaton gravity, i.e. an effective field theory that can be derived as a low-energy limit of string theory in four dimensions. |
Monday, April 17, 2023 4:45PM - 4:57PM |
Q09.00006: Black hole simulations in massive dynamical Chern-Simons gravity Chloe Richards, Alexandru Dima, Helvi Witek Astrophysical black holes (BHs) provide a laboratory to test deviations from Einstein’s General Relativity (GR); for instance, no-hair theorems state that BHs in GR are parameterized by only three conserved quantities: mass, angular momentum, and electromagnetic charge. As an example, previous authors have considered massive scalar fields evolving in GR around a BH to investigate the violation of no-hair theorems via the formation of scalar clouds. Similarly, rotating BHs in modified theories of gravity, such as dynamical Chern-Simons (dCS) gravity, have been considered to investigate the formation of scalar “hair”. In this talk, I will combine the two efforts and present numerical simulations of a massive scalar field in dCS gravity evolving in the background of a Kerr BH. From these simulations, I will explore the effect of non-minimal coupling to curvature via the Pontryagin density on the massive scalar field as well as the effect of the massive scalar field on the evolution of dCS hair. Finally, I will investigate the spectrum of characteristic frequencies in massive dCS gravity from our numerical simulations and compare it with the spectrum of characteristic frequencies in GR. |
Monday, April 17, 2023 4:57PM - 5:09PM |
Q09.00007: Binary Black Hole Mergers in a Massive Scalar Field Cloud Cheng-Hsin Cheng, Giuseppe Ficarra, Helvi Witek Ultra-light bosonic fields arising from string theory stand as compelling candidates for wave dark matter, and their presence around a binary black hole (BBH) can alter the binary dynamics significantly through processes such as superradiance, accretion, and dynamical friction. In this work, we investigate the impact of a massive scalar field on the gravitational radiation emitted during the binary black hole coalescence. This is accomplished by performing numerical relativity simulations of the full Einstein-Klein-Gordon system, where we treat the back-reaction of the scalar field onto the spacetime consistently in both the initial data and evolution. In particular, we vary the scalar mass parameter and binary mass ratio in our simulations and investigate their impacts on the coalescence waveforms, carefully detangling the effects of orbital eccentricity to draw comparisons with the vacuum scenario. We then discuss the implications of our results for gravitational wave observations. |
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