Symmetries in collective neutrino oscillations

TL;DR

This paper explores the role of symmetries in collective neutrino oscillations, analyzing how these symmetries influence spectral features and the conditions under which collective modes persist or break down in astrophysical environments.

Contribution

It establishes a criterion for significant flavor transformation based on collective precession modes and examines how anisotropy and density affect these oscillations.

Findings

Spectral swaps arise in homogeneous, isotropic conditions.

Non-collective modes decohere when symmetry breaks down.

The criterion helps predict oscillation suppression in dense, anisotropic media.

Abstract

We discuss the relationship between a symmetry in the neutrino flavour evolution equations and neutrino flavour oscillations in the collective precession mode. This collective precession mode can give rise to spectral swaps (splits) when conditions can be approximated as homogeneous and isotropic. Multi-angle numerical simulations of supernova neutrino flavour transformation show that when this approximation breaks down, non-collective neutrino oscillation modes decohere kinematically, but the collective precession mode still is expected to stand out. We provide a criterion for significant flavour transformation to occur if neutrinos participate in a collective precession mode. This criterion can be used to understand the suppression of collective neutrino oscillations in anisotropic environments in the presence of a high matter density. This criterion is also useful in understanding the breakdown of the collective precession mode when neutrino densities are small.