Bulk viscosity of nuclear matter with pions in the neutrino-trapped regime

Journal Article · 06 January 2025 · Physical Review. C

DOI: https://doi.org/10.1103/physrevc.111.015802 · OSTI ID:2496228

Harris, Steven P.  ^[1]; Fore, Bryce  ^[2]; Reddy, Sanjay  ^[3]

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1. Indiana University, Bloomington, IN (United States); University of Washington, Seattle, WA (United States); Indiana University
2. Argonne National Laboratory (ANL), Argonne, IL (United States)
3. University of Washington, Seattle, WA (United States)

Recent work has shown that a population of thermal pions could modify the equation of state and transport properties of hot and dense neutron-rich matter and introduce new reaction pathways to change the proton fraction. In this article we study their impact on the bulk viscosity of dense matter, focusing on the neutrino-trapped regime that would be realized in neutron star mergers and supernovae. We find that the presence of a thermal population of pions alters the bulk viscosity by modifying the EoS (via the susceptibilities) and by providing new reaction pathways to achieve beta equilibrium. In neutron star merger conditions, the bulk viscosity in neutrino-trapped npeμ matter (without pions) has its peak at temperatures of at most a couple MeV and is quite small at temperatures of tens of MeV. We find that thermal pions enhance the low-temperature peak of the bulk viscosity by a factor of a few and shift it to slightly lower temperatures. At higher temperatures, where the pion abundance is large but the bulk viscosity is traditionally small, pions can increase the bulk viscosity by an order of magnitude or more, although it is still orders of magnitude smaller than its peak value.

• Research Organization: Indiana University, Bloomington, IN (United States)
• Sponsoring Organization: National Science Foundation (NSF); USDOE Office of Science (SC), Nuclear Physics (NP)
• Grant/Contract Number: AC02-06CH11357; FG02-00ER41132
• OSTI ID: 2496228
• Journal Information: Physical Review. C, Journal Name: Physical Review. C Journal Issue: 1 Vol. 111; ISSN 2469-9985
• Publisher: American Physical Society (APS)Copyright Statement
• Country of Publication: United States
• Language: English