The multi-angle instability in dense neutrino systems

TL;DR

This paper investigates how angular dependencies in dense neutrino systems lead to instabilities that accelerate flavor exchange, with implications for supernova core dynamics.

Contribution

It identifies and characterizes angular-dependent instabilities in neutrino flavor evolution, providing a detailed analysis and numerical demonstrations.

Findings

Angular dependence causes flavor exchange instabilities.

Instabilities significantly speed up flavor conversion.

Implications for supernova neutrino behavior.

Abstract

We calculate rates of flavor exchange within clouds of neutrinos interacting with each other through the standard model coupling, assuming a conventional mass matrix. For cases in which there is an angular dependence in the relation among intensity, flavor and spectrum, we find instabilities in the evolution equations and greatly speeded-up flavor exchange. The instabilities are categorized by examining linear perturbations to simple solutions, and their effects are exhibited in complete numerical solutions to the system. The application is to the region just under the neutrino surfaces in the supernova core.