Corrected Beta-Equilibrium in Neutron Star Mergers

In the neutrino-transparent regime of neutron star mergers, where the temperature is about 1 to 10 MeV, the traditional cold beta equilibrium condition is incorrect. We calculate the correction term, which is the isospin chemical potential, and it reaches 20 to 30 MeV, depending on the equation of state. In order to do so, we improve the existing direct Urca rate calculations using a relativistic dispersion relation and compute the full twelve-dimensional phase space integral.