Beta equilibrium under neutron star merger conditions

TL;DR

This paper calculates temperature-dependent corrections to beta equilibrium in nuclear matter relevant for neutron star mergers, highlighting their importance for accurate Urca rate calculations.

Contribution

It introduces a consistent relativistic mean field model approach to compute nonzero-temperature corrections to beta equilibrium in neutron star merger conditions.

Findings

Nonzero-temperature correction can be 10-20 MeV.

Neglecting this correction leads to Urca rate errors by factors of 10 or more.

Relativistic dispersion relations are essential in the models.

Abstract

We calculate the nonzero-temperature correction to the beta equilibrium condition in nuclear matter under neutron star merger conditions, in the temperature range $1\,$MeV$ < T \lesssim 5\,$MeV. We improve on previous work by using a consistent description of nuclear matter based on the IUF and SFHo relativistic mean field models. This includes using relativistic dispersion relations for the nucleons, which we show is essential in these models. We find that the nonzero-temperature correction can be of order $10$ to $20\,$MeV, and plays an important role in the correct calculation of Urca rates, which can be wrong by factors of $10$ or more if it is neglected.