Charged-current neutrino interactions in core-collapse supernovae in a virial expansion

Core-collapse supernovae may depend sensitively on charged-current neutrino interactions in warm, low-density, neutron-rich matter. A proton in neutron-rich matter is more tightly bound than is a neutron. This energy shift ΔU increases the electron energy in ν_e+n→p+e, increasing the available phase space and absorption cross section. Likewise ΔU decreases the positron energy in ν_̄e+p→n+e ⁺, decreasing the phase space and cross section. We have calculated ΔU using a model-independent virial expansion and we find that ΔU is much larger, at low densities, than the predictions of many mean-field models. Therefore ΔU could have a significant impact on charged-current neutrino interactions in supernovae. Preliminary simulations of the accretion phase of core-collapse supernovae find that ΔU increases ν_̄e energies and decreases the ν_e luminosity.