Self-consistency in models of neutrino scattering and fast flavor conversion

TL;DR

This paper investigates the conflicting results of neutrino scattering effects on fast flavor conversion, emphasizing the importance of self-consistency and questioning the astrophysical relevance of scattering-enhanced flavor conversion.

Contribution

The study clarifies the role of self-consistency in modeling neutrino scattering effects and demonstrates that scattering-enhanced flavor conversion may be an artifact of simplified models.

Findings

Scattering can enhance flavor conversion in homogeneous models.

Isotropization of angular distributions causes the apparent enhancement.

Self-consistent models do not support the enhancement effect.

Abstract

Several recent numerical studies have examined the effects of neutrino neutral-current scattering on fast flavor conversion (FFC). Those studies are in apparent conflict, with some finding enhancement of flavor conversion and others finding suppression. The ones that report enhancement all use homogeneous models, and we discuss in detail the self-consistency issues that they face as a result. We reproduce scattering-enhanced FFC in our own homogeneous calculations, showing that it occurs for both neutral- and charged-current scattering and that it is due to isotropization of the angular distributions over time. Because this is the very feature of the calculations that is not self-consistent, we conclude that the enhancement effect is of unclear astrophysical relevance and may not occur in natural environments.