Beta equilibrium in neutron star mergers

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.

Comments: Section on neutrino mean free paths added. Discussion and plot of effect of isospin chemical potential on beta-equilibrium proton fraction added