Self-induced temporal instability from a neutrino antenna

TL;DR

This paper investigates how neutrino flavor compositions can spontaneously develop time-dependent pulsations due to self-interactions, revealing cascade instabilities and nonlinear effects that lead to significant flavor conversions.

Contribution

It provides a detailed analysis of temporal instabilities in a neutrino antenna model, combining numerical simulations with linear stability analysis to understand nonlinear flavor evolution.

Findings

Temporal instabilities occur with various frequencies in the model.

Linear analysis agrees with numerical results in the linear regime.

Nonlinear interactions accelerate flavor conversions significantly.

Abstract

It has been recently shown that the flavor composition of a self-interacting neutrino gas can spontaneously acquire a time-dependent pulsating component during its flavor evolution. In this work, we perform a more detailed study of this effect in a model where neutrinos are assumed to be emitted in a two-dimensional plane from an infinite line that acts as a neutrino antenna. We consider several examples with varying matter and neutrino densities and find that temporal instabilities with various frequencies are excited in a cascade. We compare the numerical calculations of the flavor evolution with the predictions of linearized stability analysis of the equations of motion. The results obtained with these two approaches are in good agreement in the linear regime, while a dramatic speed-up of the flavor conversions occurs in the non-linear regime due to the interactions among the different pulsating modes. We show that large flavor conversions can take place if some of the temporal modes are unstable for long enough, and that this can happen even if the matter and neutrino densities are changing, as long as they vary slowly.