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Evaluating radiation transport errors in merger simulations using a Monte Carlo algorithm

Foucart, F. and Duez, M. D. and Kidder, L. E. and Nguyen, R. and Pfeiffer, H. P. and Scheel, M. A. (2018) Evaluating radiation transport errors in merger simulations using a Monte Carlo algorithm. Physical Review D, 98 (6). Art. No. 063007. ISSN 2470-0010. doi:10.1103/PhysRevD.98.063007.

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Neutrino-matter interactions play an important role in the postmerger evolution of neutron star-neutron star and black hole-neutron star mergers. Most notably, they determine the properties of the bright optical/infrared transients observable after a merger. Unfortunately, Boltzmann’s equations of radiation transport remain too costly to be evolved directly in merger simulations. Simulations rely instead on approximate transport algorithms with unquantified modeling errors. In this paper, we use for the first time a time-dependent general relativistic Monte Carlo (MC) algorithm to solve Boltzmann’s equations and estimate important properties of the neutrino distribution function ∼ 10     ms after a neutron star merger that resulted in the formation of a massive neutron star surrounded by an accretion disk. We do not fully couple the MC algorithm to the fluid evolution, but use a short evolution of the merger remnant to critically assess errors in our approximate gray two-moment transport scheme. We demonstrate that the analytical closure used by the moment scheme is highly inaccurate in the polar regions, but performs well elsewhere. While the average energy of polar neutrinos is reasonably well captured by the two-moment scheme, estimates for the neutrino energy become less accurate at lower latitudes. The two-moment formalism also overestimates the density of neutrinos in the polar regions by ∼ 50 % , and underestimates the neutrino pair-annihilation rate at the poles by factors of 2–3. Although the latter is significantly more accurate than one might have expected before this study, our results indicate that predictions for the properties of polar outflows and for the creation of a baryon-free region at the poles are likely to be affected by errors in the two-moment scheme, thus limiting our ability to reliably model kilonovae and gamma-ray bursts.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Foucart, F.0000-0003-4617-4738
Duez, M. D.0000-0002-0050-1783
Kidder, L. E.0000-0001-5392-7342
Pfeiffer, H. P.0000-0001-9288-519X
Additional Information:© 2018 American Physical Society. Received 8 June 2018; published 11 September 2018. The authors thank the members of the SXS Collaboration for helpful discussions over the course of this project. F. F. acknowledges support from NASA through Grant No. 80NSSC18K0565. M. D. acknowledges support through NSF Grant No. PHY-1402916. H. P. gratefully acknowledges support from the NSERC Canada, the Canada Research Chairs Program and the Canadian Institute for Advanced Research. L. K. acknowledges support from NSF Grant No. PHY-1606654, and M. S. from NSF Grants No. PHY-1708212, No. PHY-1708213, and No. PHY-1404569. L. K. and M. S. also thank the Sherman Fairchild Foundation for their support. Computations were performed on the supercomputer Briarée from the Université de Montréal, managed by Calcul Québec and Compute Canada. The operation of these supercomputers is funded by the Canada Foundation for Innovation (CFI), NanoQuébec, RMGA and the Fonds de recherche du Québec—Nature et Technologie (FRQ-NT). Computations were also performed on the Zwicky and Wheeler clusters at Caltech, supported by the Sherman Fairchild Foundation and by NSF Award No. PHY-0960291.
Group:TAPIR, Walter Burke Institute for Theoretical Physics
Funding AgencyGrant Number
Natural Sciences and Engineering Research Council of Canada (NSERC)UNSPECIFIED
Canada Research Chairs ProgramUNSPECIFIED
Canadian Institute for Advanced Research (CIFAR)UNSPECIFIED
Sherman Fairchild FoundationUNSPECIFIED
Canada Foundation for InnovationUNSPECIFIED
Fonds de recherche du Québec - Nature et technologies (FRQNT)UNSPECIFIED
Issue or Number:6
Record Number:CaltechAUTHORS:20180911-081808846
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:89515
Deposited By: Tony Diaz
Deposited On:11 Sep 2018 16:22
Last Modified:16 Nov 2021 00:36

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