Supernova Neutrino Opacities
  In a supernova (SN) core during infall and after collapse, neutrinos are trapped by their interactions with nucleons. For the axial-vector current interactions it is not enough to include static particle-particle correlations. Even the single-nucleon spin autocorrelation reduces the scattering cross section dramatically. Therefore, the dynamical structure of the spin-density structure function has an important impact on neutrino transport in supernovae. At the present time, SN neutrino opacities cannot be calculated to a controlled degree of precision. 
Georg G. Raffelt (MPI f. Physik, Munich)