Neutrino-Mass-Driven Instabilities as the Earliest Flavor Conversion in Supernovae

TL;DR

This paper investigates how neutrino mass-driven instabilities trigger early flavor conversions in supernovae, emphasizing the importance of initial spectral crossings and their impact on subsequent fast instabilities.

Contribution

It introduces a new understanding of the timing and conditions for neutrino flavor instabilities in supernovae, highlighting the role of spectral crossings before fast instabilities develop.

Findings

Spectral crossings appear within 20 ms of collapse.

Early slow instabilities alter conditions for later fast instabilities.

Post-processing simulations may miss critical early flavor conversions.

Abstract

Collective neutrino flavor conversions in core-collapse supernovae (SNe) begin with instabilities, initially triggered when the dominant $\nu_e$ outflow concurs with a small antineutrino flux of opposite lepton number, with $\overline{\nu}_e$ dominating over $\overline{\nu}_\mu$. When these "flipped" neutrinos emerge in the energy-integrated angular distribution (angular crossing), they initiate a fast instability. However, before such conditions arise, spectral crossings typically appear within $20~\mathrm{ms}$ of collapse, i.e., local spectral excesses of $\overline{\nu}_e$ over $\overline{\nu}_\mu$ along some direction. Therefore, post-processing SN simulations cannot consistently capture later fast instabilities because the early slow ones have already altered the conditions.