Fast Flavor Depolarization of Supernova Neutrinos

TL;DR

This paper develops a theoretical framework for understanding how fast collective neutrino oscillations in supernovae lead to flavor depolarization, affecting neutrino signals and supernova evolution.

Contribution

It introduces a theory of fast flavor depolarization, detailing how neutrino flavor differences diminish through diffusion to smaller angular scales and providing a method to compute depolarized fluxes.

Findings

Depolarization occurs due to diffusion to smaller angular scales.

Transverse relaxation determines the epoch of irreversible depolarization.

An explicit formula for depolarized fluxes is provided.

Abstract

Flavor-dependent neutrino emission is critical to the evolution of a supernova and its neutrino signal. In the dense anisotropic interior of the star, neutrino-neutrino forward-scattering can lead to fast collective neutrino oscillations, which has striking consequences. We present a theory of fast flavor depolarization, explaining how neutrino flavor differences become smaller, i.e., depolarize, due to diffusion to smaller angular scales. We show that transverse relaxation determines the epoch of this irreversible depolarization. We give a method to compute the depolarized fluxes, presenting an explicit formula for simple initial conditions, which can be a crucial input for supernova theory and neutrino phenomenology.