MURCA driven Bulk viscosity in neutrino trapped baryonic matter

TL;DR

This paper investigates how trapped neutrinos influence bulk viscosity in dense baryonic matter during binary neutron star mergers, revealing temperature-dependent resonant behavior and implications for post-merger dynamics.

Contribution

It introduces a detailed analysis of neutrino effects on bulk viscosity using relativistic mean field models and evaluates the dissipation timescales relevant for neutron star merger remnants.

Findings

Bulk viscosity exhibits resonant peaks within 13-50 MeV temperature range.

Presence of neutrinos shifts the viscosity peak to higher temperatures.

Viscous dissipation timescales range from 32 to 100 milliseconds.

Abstract

We examine bulk viscosity, taking into account trapped neutrinos in baryonic matter, in the context of binary neutron star mergers. Following the merging event, the binary star can yield a remnant compact object with densities up to $5$ nuclear saturation density and temperature upto $50$ MeV resulting in the retention of neutrinos. We employ two relativistic mean field models, NL3 and DDME2, to describe the neutrino-trapped baryonic matter. The dissipation coefficient is determined by evaluating the Modified URCA interaction rate in the dense baryonic medium, and accounting for perturbations caused by density oscillations. We observe the resonant behavior of bulk viscosity as it varies with the temperature of the medium. The bulk viscosity peak remains within the temperature range of $\sim 13-50$ MeV, depending upon the underlying equation of states and lepton fractions. This temperature range corresponds to the relevant domain of binary neutron star mergers. We also note that in presence of neutrinos in the medium the bulk viscosity peak shifts towards higher temperature and the peak value of bulk viscosity also changes. The time scale of viscous dissipation is dictated by the beta-off-equilibrium susceptibilities derived from the nuclear equation of state. The resulting viscous decay time scale ranges from $32-100$ milliseconds, which aligns with the order of magnitude of the post-merger object's survival time in some specific scenarios.