Consistent Treatment of Muons in Binary Neutron Star Mergers

TL;DR

This paper introduces advanced numerical simulations of binary neutron star mergers that include muons and their reactions, assessing their impact on astrophysical outcomes and neutrino interactions.

Contribution

It develops a comprehensive treatment of muons and muonic reactions in neutron star merger simulations, employing novel neutrino rate calculations and a two-timescale approach.

Findings

Muon inclusion slightly alters ejecta properties, reducing mass by up to 17%.

Remnant evolution and outflow characteristics are largely unaffected by muons.

Neutrino-matter equilibration is effectively modeled with the new two-timescale method.

Abstract

We present a set of numerical-relativity binary neutron star merger simulations incorporating muons and muonic reactions for two baseline baryonic equations-of-state. In order to investigate the possible impact of muons and muonic weak reactions, we treat neutrinos with a gray (energy-independent) truncated moments scheme and an implicit-explicit time integrator. Newly computed neutrino rates are employed within the full kinematics approach for a set of relevant reactions, and pair-processes are modeled via opacities computed using reaction kernels, that allow a consistent treatment of neutrino interaction rates. We find that equilibration between matter and radiation is successfully captured by a novel two timescales approach. Of astrophysical interest is the general agreement between our muonic and non-muonic results regarding the remnant evolution, disk and outflow properties. Average electron fractions, asymptotic velocities and temperatures are different by less than $\sim 6\%$, while the main impact of muons is a reduction in ejecta masses by at most $\sim 17\%$. Therefore, based on our findings, accounting for the presence of muons and muonic reactions might result much less severe consequences regarding nucleosynthetic yields and electromagnetic counterparts than previously reported in the literature.