Inelastic neutrino scattering off hot nuclei in supernova environments

Abstract

We study inelastic neutrino scattering off hot nuclei for temperatures relevant under supernova conditions. The method we use is based on the quasiparticle random phase approximation extended to finite temperatures within the thermo-field dynamics. The method allows a transparent treatment of upward and downward transitions in hot nuclei, avoiding the application of Brink's hypothesis. For the sample nuclei ${}^{56}$Fe and ${}^{82}$Ge we perform a detailed analysis of thermal effects on the strength distributions of allowed Gamow-Teller (GT) transitions which dominate the scattering process at low neutrino energies. For ${}^{56}$Fe and ${}^{82}$Ge the finite temperature cross sections are calculated by taking into account the contribution of allowed and forbidden transitions. The observed enhancement of the cross section at low neutrino energies is explained by considering thermal effects on the GT strength. For ${}^{56}$Fe we compare the calculated cross sections to those obtained earlier from a hybrid approach that combines large-scale shell-model and RPA calculations.