Neutrino-neutrino scattering and matter-enhanced neutrino flavor transformation in supernovae

The authors examine matter-enhanced neutrino flavor transformation (ντ(μ)left-equilibrium νe) in the region above the neutrino sphere in Type II supernovae. Their treatment explicitly includes contributions to the neutrino-propagation Hamiltonian from neutrino-neutrino forward scattering. A proper inclusion of these contributions shows that they have a completely negligible effect on the range of νe-ντ(μ) vacuum mass-squared difference, δm2, and vacuum mixing angle, θ, or equivalently sin2θ, required for enhanced supernova shock re-heating. When neutrino background effects are included, the authors find that r-process nucleosynthesis from neutrino-heated supernova ejecta remains a sensitive probe of the mixing between a light νe and a ντ(μ) with a cosmologically significant mass. Neutrino-neutrino scattering contributions are found to have a generally small effect on the (δm2, sin2θ) parameter region probed by r-process nucleosynthesis. They point out that the nonlinear effects of the neutrino background extend the range of sensitivity of reprocess nucleosynthesis to smaller values of δm2