Neutrino transport in supernova models: a multigroup, flux limited diffusion scheme

A multigroup, diffusion scheme is derived from the Boltzmann equation for efficient numerical computation of neutrino transport in a collapsing stellar core. This scheme treats all neutrino scattering processes correctly with a Legendre expansion of the scattering rates. Modifications of the diffusion coefficient and the addition of a flux limiter extend the applicability of the scheme to neutrino transparent regimes and improve the agreement of the solution in both opaque and transparent regimes with those obtained analytically for some test problems. In addition, a more accurate treatment of the neutrino flow across shock discontinuities is developed through a shock matching condition. The solutions given by this multigroup, flux-limited diffusion scheme are compared with those of a modified Ssub(N) code. (Auth.)