Bulletin of the American Physical Society
APS April Meeting 2022
Volume 67, Number 6
Saturday–Tuesday, April 9–12, 2022; New York
Session T13: Mini-Symposium: Finite Temperature and Transport Phenomena in Neutron Star MergersMini-Symposium Recordings Available
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Sponsoring Units: DNP Chair: Jacquelyn Noronha-Hostler, University of Illinois at Urbana-Champaign Room: Empire |
Monday, April 11, 2022 3:45PM - 4:21PM |
T13.00001: Finite Temperature Effects in Neutron Star Mergers Invited Speaker: Carolyn Raithel Binary neutron star mergers provide a unique laboratory for studying the dense-matter equation of state (EOS) across a wide range of parameter space, from the cold EOS during the inspiral to the finite-temperature EOS following the merger. In this talk, I will discuss the impact of uncertainties in the finite-temperature part of the EOS on the post-merger phase of a binary neutron star coalescence, during which time the matter is heated to significant temperatures and can deviate away from its initial equilibrium composition. I will present a new set of neutron star merger simulations, which use a parametrized framework for calculating the EOS at arbitrary temperatures and compositions. I will discuss how systematically varying the properties of the particle effective mass affects the thermal profile of the post-merger remnant and how this, in turn, influences the post-merger dynamics and gravitational wave emission. |
Monday, April 11, 2022 4:21PM - 4:33PM |
T13.00002: Monte-Carlo radiation transport in neutron star merger simulations Francois V Foucart Neutron star mergers provide us with a remarkable laboratory to test the laws of physics in dense environments, to constrain the production sites of heavy elements, and to understand high-energy transients like gamma-ray bursts. Neutrinos play an important role in these mergers: they are the main source of cooling in post-merger remnants, and the main drivers of changes to the composition of the matter that they eject. As a result, neutrino-matter interactions significantly impact the outcome of nucleosynthesis in mergers, and the properties of the optical/infrared transients that they power. Most merger simulations to-date have however treated neutrinos using approximate transport methods – either "leakage" of "moment" schemes. Here, I will discuss the implementation in the SpEC code of a Monte-Carlo transport scheme, the challenges associated with the use of such an algorithm in merger simulations, and its application so far to simulations of NSNS and NSBH mergers. These simulations allow us to provide improved estimates for the properties of the baryonic matter ejected by mergers and of the neutrinos escaping merger remnants. Comparisons with simulations using approximate transport algorithms also allow us to estimate uncertainties in these approximate transport schemes. |
Monday, April 11, 2022 4:33PM - 4:45PM |
T13.00003: A New General Relativistic, Magnetohydrodynamics, Radiation Transport Code For Dynamical Spacetimes Lunan Sun We describe our new radiative transport module that we implemented in the Illinois GRMHD code. The module employs the general relativistic truncated moment ("M1") formalism, which uses an analytic expression to close the radiation moment equations and smoothly interpolates between optically thin and thick limits. We tested the scheme by simulating thermal Oppenheimer-Synder collapse to a black hole and find we can reliably reproduce the results in previous studies that could only treat transport in the optically thick interior. However, our M1 scheme can also track the emitted radiation into the optically thin exterior and correctly determines the emission as viewed by a distant observer. We then employ our code to treat the full GRMHD-neutrino transport evolution of a merging binary neutron star system. Two versions are considered: a "simple" one that evolves a single neutrino species (electron anti-neutrino) and considers only charged-current processes and another "complete" one that evolves all three species (electron neutrino, electron anti-neutrino, and heavy-lepton neutrino) with all relevant interactions. Preliminary results will be presented. |
Monday, April 11, 2022 4:45PM - 4:57PM |
T13.00004: Unified Approach to In-Medium Beta Decay Alexander Haber, Ziyuan Zhang, Mark G Alford, Steven P Harris Weak processes like neutron decay and electron capture play a fundamental role in transport properties of neutron stars and binary neutron star mergers. In dense nuclear matter, these processes are dominated by particles on the Fermi surface and called direct and modified Urca processes. Traditionally, these processes are computed separately and semi analytically, using various approximations. In this work we will present a new unified approach to modified and direct Urca. This new approach allows us to go beyond the Fermi surface approximation and to fundamentally improve the in-medium calculation of weak decays by including the nucleon width. |
Monday, April 11, 2022 4:57PM - 5:09PM |
T13.00005: A Unified Approach to Urca Processes Ziyuan Zhang, Mark G Alford, Alexander Haber, Steven P Harris Weak decay processes (like direct and modified Urca) play an important role in transport phenomena in neutron stars and neutron star mergers. The traditional treatment for the in-medium nucleon propagator in the modified Urca process uses crude approximations. We are developing an approach to unify direct and modified Urca processes by including the nucleon widths. This potentially allows us to improve several aspects of the Urca rates, which can influence cooling, bulk viscosity and other dissipative processes. |
Monday, April 11, 2022 5:09PM - 5:21PM |
T13.00006: Conservative finite volume scheme for BDNK relativistic dissipative hydrodynamics Alex Pandya, Elias R Most, Frans Pretorius We present the first conservative finite volume numerical scheme for the equations of BDNK theory, a promising framework for incorporating dissipative effects such as viscosity and heat conduction into relativistic fluid models. Such effects have been shown to be important in modeling the quark-gluon plasma produced in heavy-ion collisions, and recent studies have suggested that they may also be needed to model binary neutron star mergers at the level of accuracy required for next-generation gravitational wave detectors. Our scheme serves as an early step toward the application of BDNK theory to systems such as these, and has been designed to possess the same enhanced accuracy and stability properties typically required of relativistic ideal fluid solvers. In this talk, I briefly review BDNK theory, outline the construction of the scheme, highlight its behavior in a suite of multidimensional test problems, and comment on directions for future work. |
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