Fast collective neutrino oscillations inside the neutrino sphere in core-collapse supernovae

Neutrinos are believed to have a key role in the explosion mechanism of core-collapse supernovae as they carry most of the energy released by the gravitational collapse of a massive star. If their flavor is converted fast inside the neutrino sphere, the supernova explosion may be influenced. This paper is reporting the results of the extended work of our previous paper. We perform a thorough survey of the ELN crossing in one of our self-consistent, realistic Boltzmann simulations in two spatial dimensions under axisymmetry for the existence of the crossings between ν_eand ν_eangular distributions, or the electron lepton number (ELN) crossing. We report for the first time the positive detections deep inside the core of the massive star in the vicinity of neutrino sphere at r ≈ 16 - 21 km. We find that the appearance of light elements enhances the chemical potential difference between proton and neutron, which mitigates the Fermi-degeneracy of ν_eand facilitates the ELN crossing. Since the region of positive detection are sustained and, in fact, expanding with time, it may have an impact on the explosion of core-collapse supernovae, observational neutrino astronomy and nucleosynthesis of heavy nuclei.