Collective neutrino-flavor oscillations and application to supernova nucleosynthesis

Abstract

There are still poorly known non-linear effects caused by coherent scatterings of self-interacting neutrinos emitted from the proto-neutron star in core-collapse supernovae. One of these effects manifests itself in flavor space as collective neutrino-flavor oscillation, which results in a dramatic change in energy spectra of neutrinos. This could affect the explosive nucleosynthesis such as r-process and nu- and rp-processes in neutron-rich and proton-rich environments, respectively. We study the neutrino flavor change due to collective oscillations in the 3 flavor and multi-angle calculations and estimate the electron mole fraction Ye that is relevant for explosive nucleosynthesis. The results are compared with those calculated by assuming a single-angle approximation which ignores the angular dependence in density matrices of neutrinos. We then find that in multi-angle case, the onset of the collective oscillation delays compared with single-angle case and that the oscillation effects in Ye evolution are negligible. These results of numerical simulation suggest that the single-angle approximation is not necessarily a good approximation and that one has to carry out multi-angle calculations in order to obtain numerically reliable and physically realistic result of collective neutrino-flavor oscillations.