A change of direction in pairwise neutrino conversion physics: The effect of collisions

TL;DR

This paper investigates how collisions influence fast neutrino flavor conversions in dense astrophysical environments, revealing that collisions can unexpectedly enhance these conversions, emphasizing the importance of self-consistent modeling.

Contribution

It introduces a simplified framework showing that collisions may promote, rather than suppress, neutrino flavor conversions, challenging previous assumptions.

Findings

Collisions can enhance fast neutrino flavor conversions.

Self-consistent treatment of collisions is crucial for accurate predictions.

Collisions may have a counterintuitive role in neutrino flavor dynamics.

Abstract

Fast pairwise conversions of neutrinos may affect the flavor distribution in the core of neutrino-dense sources. We explore the interplay between collisions and fast conversions within a simplified framework that assumes angle-independent, direction-changing collisions in a neutrino gas that has no spatial inhomogeneity. Counter to expectations, we find that collisions may enhance fast flavor conversions instead of damping them. Our work highlights the need to take into account the feedback of collisions on the neutrino angular distributions self-consistently, in order to predict the flavor outcome in the context of fast pairwise conversions reliably.