Flavor instabilities in the neutrino line model

TL;DR

This paper demonstrates that removing symmetry assumptions in the neutrino line model reveals new collective flavor oscillation behaviors, indicating that real astrophysical environments may exhibit more complex neutrino dynamics than previously modeled.

Contribution

It shows that breaking spatial and directional symmetries in the neutrino line model leads to the development of collective oscillations in regimes previously considered stable.

Findings

Collective oscillations can occur without symmetry constraints.

Symmetry-breaking leads to qualitatively different neutrino behaviors.

Implications for modeling neutrino dynamics in supernovae and accretion disks.

Abstract

A dense neutrino medium can experience collective flavor oscillations through nonlinear neutrino-neutrino refraction. To make this multi-dimensional flavor transport problem more tractable, all existing studies have assumed certain symmetries (e.g., the spatial homogeneity and directional isotropy in the early universe) to reduce the dimensionality of the problem. In this work we show that, if both the directional and spatial symmetries are not enforced in the neutrino line model, collective oscillations can develop in the physical regimes where the symmetry-preserving oscillation modes are stable. Our results suggest that collective neutrino oscillations in real astrophysical environments (such as core-collapse supernovae and black-hole accretion discs) can be qualitatively different from the predictions based on existing models in which spatial and directional symmetries are artificially imposed.