Beta equilibrium in neutron star mergers

TL;DR

This paper demonstrates that the standard criterion for beta equilibrium in neutron star mergers is invalid at high temperatures, and proposes a revised criterion involving an isospin chemical potential that varies with neutrino trapping conditions.

Contribution

It introduces a new criterion for beta equilibrium in hot, neutrino-transparent nuclear matter relevant to neutron star mergers, correcting previous assumptions.

Findings

Standard beta equilibrium criterion fails above 1 MeV temperature.

Isospin chemical potential can reach 10-20 MeV in mergers.

Revised criterion depends on neutrino trapping temperature.

Abstract

We show that the commonly used criterion for beta equilibrium in neutrino-transparent dense nuclear matter becomes invalid as temperatures rise above 1 MeV. Such temperatures are attained in neutron star mergers. By numerically computing the relevant weak interaction rates we find that the correct criterion for beta equilibrium requires an isospin chemical potential that can be as large as 10-20 MeV, depending on the temperature at which neutrinos become trapped.