Fast Flavor Oscillations of Astrophysical Neutrinos with $1,\,2,\,\ldots,\,\infty$ Crossings

TL;DR

This paper investigates how the number of electron lepton number crossings influences fast neutrino flavor oscillations in dense astrophysical environments, revealing that many crossings can suppress oscillations and stabilize neutrino flavor composition.

Contribution

It provides a two-dimensional analysis showing the impact of multiple ELN crossings on fast flavor oscillations, highlighting a potential self-limiting stabilization mechanism.

Findings

Multiple ELN crossings can inhibit flavor oscillations.

High density environments tend to have similar angular distributions, leading to crossings mainly from fluctuations.

The stabilization mechanism is relevant for early Universe and supernova conditions.

Abstract

In the early Universe, as well as in supernovae and merging neutron stars, neutrinos have such high densities that they affect each other and exhibit collective flavor oscillations. A crucial ingredient for fast collective flavor oscillations is that the electron lepton number (ELN) distribution changes its sign as a function of direction, i.e., has a zero crossing. We present a study in two dimensions and show how fast flavor oscillations depend on the ELN and its crossings. We show that a large number of crossings can inhibit flavor oscillations. This may be a natural self-limiting mechanism that stabilizes the flavor content of the dense neutrino gas in a vast majority of scenarios, especially the early Universe, where the angular distributions for all flavors are very similar and crossings occur mainly due to fluctuations.