Reduction of neutrino-nucleon scattering rate by nucleon-nucleon collisions

We studied possible modifications of the neutrino-nucleon scattering rate due to the nucleon-nucleon collisions in the hot dense matter which we find in the supernova core. We show that the finite width of the nucleon spectral function induced by the nucleon collisions leads to a broadening of the dynamical spin structure function of the nucleon, resulting in a reduction of the rate of neutrino-nucleon scattering via the axial vector current and making the energy exchange between neutrinos and nucleons easier. The reduction rate is relatively large, similar to 0.6, even at density similar to 10(13)g/cm(3) and could have a significant impact on the dynamics of the collapse-driven supernova as well as the cooling of the proto neutron star. (C) 2000 Elsevier Science B.V. All rights reserved.