Thermal and Magnetic effects on Bulk Viscosity in Binary Neutron Star Mergers

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Hauptverfasser: Tambe, Pranjal, Chatterjee, Debarati, Alford, Mark, Haber, Alexander
Format: Preprint
Veröffentlicht: 2025
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author Tambe, Pranjal
Chatterjee, Debarati
Alford, Mark
Haber, Alexander
author_facet Tambe, Pranjal
Chatterjee, Debarati
Alford, Mark
Haber, Alexander
contents Astrophysical scenarios such as binary neutron star mergers, protoneutron stars, and core-collapse supernovae involve finite temperatures and strong magnetic fields. Previous studies on the effect of magnetic fields on flavor-equilibration processes relied on the Fermi surface approximation, which is not a reliable approximation in the neutrino-transparent regime of matter in supernovae or neutron star mergers. In a recent study, we went beyond the Fermi surface approximation, performing the full phase space integral to obtain direct Urca rates in a background magnetic field. In this work, we extend these calculations to incorporate the collisional broadening (modified Urca) contribution. We use the recently developed nucleon width approximation, which naturally includes the magnetic field dependence of all contributions. We demonstrate the impact of magnetic fields on the flavor-equilibrium condition for two finite-temperature equations of state with different direct Urca thresholds. We also study the impact of magnetic fields on the bulk viscous dissipation of density oscillations relevant in postmerger scenarios.
format Preprint
id arxiv_https___arxiv_org_abs_2510_09104
institution arXiv
publishDate 2025
record_format arxiv
spellingShingle Thermal and Magnetic effects on Bulk Viscosity in Binary Neutron Star Mergers
Tambe, Pranjal
Chatterjee, Debarati
Alford, Mark
Haber, Alexander
Nuclear Theory
High Energy Astrophysical Phenomena
High Energy Physics - Phenomenology
Astrophysical scenarios such as binary neutron star mergers, protoneutron stars, and core-collapse supernovae involve finite temperatures and strong magnetic fields. Previous studies on the effect of magnetic fields on flavor-equilibration processes relied on the Fermi surface approximation, which is not a reliable approximation in the neutrino-transparent regime of matter in supernovae or neutron star mergers. In a recent study, we went beyond the Fermi surface approximation, performing the full phase space integral to obtain direct Urca rates in a background magnetic field. In this work, we extend these calculations to incorporate the collisional broadening (modified Urca) contribution. We use the recently developed nucleon width approximation, which naturally includes the magnetic field dependence of all contributions. We demonstrate the impact of magnetic fields on the flavor-equilibrium condition for two finite-temperature equations of state with different direct Urca thresholds. We also study the impact of magnetic fields on the bulk viscous dissipation of density oscillations relevant in postmerger scenarios.
title Thermal and Magnetic effects on Bulk Viscosity in Binary Neutron Star Mergers
topic Nuclear Theory
High Energy Astrophysical Phenomena
High Energy Physics - Phenomenology
url https://arxiv.org/abs/2510.09104