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

Abstract

The authors examine matter-enhanced neutrino flavor transformation ({nu}{sub {tau}({mu})}{l_equilibrium} {nu}{sub e}) 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 {nu}{sub e}-{nu}{sub {tau}({mu}}) vacuum mass-squared difference, {delta}m{sup 2}, and vacuum mixing angle, {theta}, or equivalently sin{sup 2}{theta}, 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 {nu}{sub e} and a {nu}{sub {tau}({mu})} with a cosmologically significant mass. Neutrino-neutrino scattering contributions are found to have a generally small effect on the ({delta}m{sup 2}, sin{sup 2}{theta}) 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 {delta}m{sup 2}.