  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.
