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

TL;DR

This study investigates fast neutrino flavor conversions inside the neutrino sphere of core-collapse supernovae, revealing new regions of electron lepton number crossing that could influence supernova explosions and nucleosynthesis.

Contribution

First detection of ELN crossings deep inside the supernova core using realistic simulations, highlighting their potential impact on explosion mechanisms.

Findings

ELN crossings detected at 16-21 km inside the core.

Low electron fraction and light elements promote ELN crossings.

Crossings expand and persist over time, affecting supernova dynamics.

Abstract

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 $\nu_e$ and $\bar\nu_e$ angular 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 $r$ $\approx$ 16 - 21 km. We find that low values of the electron fraction $Y_e$ produced by convective motions together with the appearance of light elements are critically important to give rise to the ELN crossing by enhancing the chemical potential difference between proton and neutron, and hence by mitigating the Fermi-degeneracy of $\nu_e$. 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.