Neutrino Opacities for Neutron Star Merger Simulations

When two neutron stars merge, matter is no longer in chemical equilibrium, prompting weak interaction processes. We present a novel calculation of neutrino opacities for neutron star merger simulations, improving on previous methods by using a relativistic matrix element and dispersion relation, and full phase space integration. We calculate neutrino opacities for processes that have the strongest impact on a high baryon-number environment: n+nup+e. Neutrino opacities, crucial for post-merger phenomena like cooling, density-oscillation damping, and mass outflow, are accurately determined using our state-of-the-art calculations. Inclusion of these opacities is essential to reduce systematic uncertainty in neutron star merger simulations.