EFFECTS OF CORRELATIONS ON NEUTRINO OPACITIES IN NUCLEAR-MATTER

Including nucleon-nucleon correlations due to both Fermi statistics an d nuclear forces, we have developed a general formalism for calculatin g the neutral-current neutrino-nucleon scattering rates in nuclear mat ter. We derive corrections to the dynamic structure factors due to bot h density and spin correlations and find that neutrino-nucleon scatter ing rates are suppressed by large factors around and above nuclear den sity. Hence, in particular for the nu(mu) and nu(tau) neutrinos, but a lso for the nu(e) neutrinos, supernova cores are more ''transparent'' than previously thought. The many-body corrections increase with densi ty, decrease with temperature, and are roughly independent of incident neutrino energy. In addition, we find that the spectrum of energy tra nsfers in neutrino scattering is considerably broadened by the interac tions in the medium. An identifiable component of this broadening come s from the absorption and emission of quanta of collective modes akin to the Gamow-Teller and giant dipole resonances in nuclei (zero sound; spin sound), with Cerenkov kinematics. Under the assumption that both the charged-current and the neutral-current cross sections are decrea sed by many-body effects, we calculate a set of ad hoc protoneutron st ar cooling models to gauge the potential importance of the new opaciti es to the supernova itself. While the early luminosities are not alter ed, the luminosities after many hundreds of milliseconds to seconds ca n be increased by factors that range from 10 to 100 %. Such enhancemen ts may have a bearing on the efficacy of the neutrino-driven supernova mechanism, the delay to explosion, the energy of the explosion, and t he strength and relative role of convective overturn at late times. Ho wever, the actual consequences, if any, of these new neutrino opacitie s remain to be determined.