Fast flavor oscillations in dense neutrino media with collisions

TL;DR

This paper studies how collisions and neutrino mass splitting influence fast neutrino oscillations in dense media, finding that such oscillations are largely unaffected on small scales but damped over larger distances, impacting supernova physics.

Contribution

It provides a detailed analysis of the effects of neutrino collisions and mass splitting on fast oscillations, highlighting their minimal impact on small scales and damping behavior at larger scales.

Findings

Fast oscillations are unaffected by small neutrino mass splitting.

Oscillations are damped over large scales due to collisions and angular distribution flattening.

Fast oscillation waves can propagate near the neutrino sphere with minimal damping.

Abstract

We investigate the impact of the nonzero neutrino splitting and elastic neutrino-nucleon collisions on fast neutrino oscillations. Our calculations confirm that a small neutrino mass splitting and the neutrino mass hierarchy have very little effect on fast oscillation waves. We also demonstrate explicitly that fast oscillations remain largely unaffected for the time/distance scales that are much smaller than the neutrino mean free path but are damped on larger scales. This damping originates from both the direct modification of the dispersion relation of the oscillation waves in the neutrino medium and the flattening of the neutrino angular distributions over time. Our work suggests that fast neutrino oscillation waves produced near the neutrino sphere can propagate essentially unimpeded which may have ramifications in various aspects of the supernova physics.