Neutrino oscillations in supernovae: angular moments and fast instabilities

TL;DR

This paper investigates the conditions under which neutrino flavor instabilities occur in supernovae, emphasizing the importance of angular distributions and providing criteria to predict such instabilities based on simulation data.

Contribution

It introduces new criteria for neutrino flavor instability onset, accounting for angular distribution effects, and analyzes nonlinear oscillations using supernova simulation data.

Findings

Zero-crossing in neutrino density difference is not sufficient for instability.

Fast oscillations depend on the angular distribution's forward-peaking.

Formulated criteria improve prediction of flavor instabilities.

Abstract

Recent theoretical work indicates that the neutrino radiation in core-collapse supernovae may be susceptible to flavor instabilities that set in far behind the shock, grow extremely rapidly, and have the potential to profoundly affect supernova dynamics and composition. Here we analyze the nonlinear collective oscillations that are prefigured by these instabilities. We demonstrate that a zero-crossing in $n_{\nu_e} - n_{\bar{\nu}_e}$ as a function of propagation angle is not sufficient to generate instability. Our analysis accounts for this fact and allows us to formulate complementary criteria. Using Fornax simulation data, we show that fast collective oscillations qualitatively depend on how forward-peaked the neutrino angular distributions are.