Collective neutrino oscillations and spontaneous symmetry breaking

TL;DR

This paper reviews the phenomenon of collective neutrino oscillations in dense astrophysical environments, highlighting how these oscillations can spontaneously break spatial and directional symmetries, challenging previous simplified models.

Contribution

It demonstrates how collective neutrino oscillations can spontaneously break symmetries in toy models, questioning the validity of symmetry-imposed assumptions in prior studies.

Findings

Collective oscillations can spontaneously break symmetries.

Simplified models may not capture the full complexity of neutrino behavior.

Symmetry breaking impacts the understanding of neutrino transport in supernovae.

Abstract

Neutrino oscillations in a hot and dense astrophysical environment such as a core-collapse supernova pose a challenging, seven-dimensional flavor transport problem. To make the problem even more difficult (and interesting), neutrinos can experience collective oscillations through nonlinear refraction in the dense neutrino medium in this environment. Significant progress has been made in the last decade towards the understanding of collective neutrino oscillations in various simplified neutrino gas models with imposed symmetries and reduced dimensions. However, a series of recent studies seem to have "reset" this progress by showing that these models may not be compatible with collective neutrino oscillations because the latter can break the symmetries spontaneously if they are not imposed. We review some of the key concepts of collective neutrino oscillations by using a few simple toy models. We also elucidate the breaking of spatial and directional symmetries in these models because of collective oscillations.