Collisional flavor swap with neutrino self-interactions

TL;DR

This paper introduces a new phenomenon called collisional flavor swap, where neutrino-matter interactions combined with self-interactions cause complete spectral exchange between neutrino flavors, potentially impacting supernova and neutron star merger physics.

Contribution

The study reveals the conditions and mechanisms for collisional flavor swaps, highlighting their occurrence due to resonance-like instabilities and their dependence on self-interaction dominance.

Findings

Collisional flavor swaps can occur across the entire neutrino energy spectrum.

Resonance-like collisional flavor instability is necessary for triggering swaps.

Energy-dependent features can emerge after flavor swaps.

Abstract

Neutrinos play pivotal roles in determining fluid dynamics, nucleosynthesis, and their observables in core-collapse supernova (CCSN) and binary neutron star merger (BNSM). In this paper, we present a novel phenomenon, collisional flavor swap, in which neutrino-matter interactions trigger the complete interchange of neutrino spectra between two different flavors, aided by neutrino self-interactions. We find that a necessary condition to trigger the collisional swap is occurrences of resonance-like collisional flavor instability. In cases where neutrino self-interactions substantially dominate over the collision rate, the collisional swap occurs in the entire neutrino energy spectrum, while intriguing energy dependent features can emerge after the completion of flavor swap. Since flavor swaps correspond to the most extreme case in flavor conversions, they have a great potential to affect CCSN and BNSM phenomena.