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

Neutrino Flavor Transformation in Supernovae Yong-Zhong Qian and George M. Fuller Institute for Nuclear Theory, HN-12 University of Washington, Seattle, WA 98195 ABSTRACT We examine matter-enhanced neutrino flavor transformation (ντ(μ) ⇀↽ νe) in the region above the neutrino sphere in Type II supernovae. Our 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, δm , and vacuum mixing angle, θ, or equivalently sin 2θ, required for enhanced supernova shock re-heating. When neutrino background effects are included, we 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 (δm, sin 2θ) parameter region probed by r-process nucleosynthesis. We point out that the nonlinear effects of the neutrino background extend the range of sensitivity of r-process nucleosynthesis to smaller values of δm. PACS numbers: 14.60.Pq, 12.15.Ff, 97.10.Cv, 97.60.Bw