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Implementation of Monte Carlo Transport in the General Relativistic SpEC Code

Foucart, Francois and Duez, Matthew D. and Hébert, François and Kidder, Lawrence E. and Kovarik, Phillip and Pfeiffer, Harald P. and Scheel, Mark A. (2021) Implementation of Monte Carlo Transport in the General Relativistic SpEC Code. Astrophysical Journal, 920 (2). Art. No. 82. ISSN 0004-637X. doi:10.3847/1538-4357/ac1737.

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Neutrino transport and neutrino−matter interactions are known to play an important role in the evolution of neutron star mergers and of their post-merger remnants. Neutrinos cool remnants, drive post-merger winds, and deposit energy in the low-density polar regions where relativistic jets may eventually form. Neutrinos also modify the composition of the ejected material, impacting the outcome of nucleosynthesis in merger outflows and the properties of the optical/infrared transients that they power (kilonovae). So far, merger simulations have largely relied on approximate treatments of the neutrinos (leakage, moments) that simplify the equations of radiation transport in a way that makes simulations more affordable but also introduces unquantifiable errors in the results. To improve on these methods, we recently published a first simulation of neutron star mergers using a low-cost Monte Carlo algorithm for neutrino radiation transport. Our transport code limits costs in optically thick regions by placing a hard ceiling on the value of the absorption opacity of the fluid, yet all approximations made within the code are designed to vanish in the limit of infinite numerical resolution. We provide here an in-depth description of this algorithm, of its implementation in the SpEC merger code, and of the expected impact of our approximations in optically thick regions. We argue that the last is a subdominant source of error at the accuracy reached by current simulations and for the interactions currently included in our code. We also provide tests of the most important features of this code.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Foucart, Francois0000-0003-4617-4738
Duez, Matthew D.0000-0002-0050-1783
Hébert, François0000-0001-9009-6955
Kidder, Lawrence E.0000-0001-5392-7342
Pfeiffer, Harald P.0000-0001-9288-519X
Scheel, Mark A.0000-0001-6656-9134
Additional Information:© 2021. The American Astronomical Society. Received 2021 March 31; revised 2021 July 6; accepted 2021 July 21; published 2021 October 18. F.F. gratefully acknowledges support from the NSF through grant PHY-1806278, from the DOE through grant DE-SC0020435, and from NASA through grant 80NSSC18K0565. M.D. gratefully acknowledges support from the NSF through grant PHY-1806207. H.P. gratefully acknowledges support from the NSERC Canada. L.K. acknowledges support from NSF grant PHY-1912081 and OAC-1931280. F.H. and M.S. acknowledge support from NSF grants PHY-170212 and PHY-1708213. F.H., L.K., and M.S. also thank the Sherman Fairchild Foundation for their support. Computations were performed on the Plasma cluster at UNH, supported by the NSF MRI program through grant No. AGS 1919310. Computations were also performed on the Wheeler cluster at Caltech, supported by the Sherman Fairchild Foundation and by Caltech.
Group:TAPIR, Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
Department of Energy (DOE)DE-SC0020435
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Sherman Fairchild FoundationUNSPECIFIED
Subject Keywords:Computational methods; Neutron stars; Neutrino astronomy; R-process
Issue or Number:2
Classification Code:Unified Astronomy Thesaurus concepts: Computational methods (1965); Neutron stars (1108); Neutrino astronomy (1100); R-process (1324)
Record Number:CaltechAUTHORS:20211026-145732583
Persistent URL:
Official Citation:Francois Foucart et al 2021 ApJ 920 82
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:111642
Deposited By: Tony Diaz
Deposited On:26 Oct 2021 15:52
Last Modified:28 Apr 2023 20:37

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