Where, when and why: occurrence of fast-pairwise collective neutrino oscillation in three-dimensional core-collapse supernova models

TL;DR

This study investigates the occurrence of fast-pairwise collective neutrino oscillations in three-dimensional core-collapse supernova models, revealing their common presence and key driving mechanisms, which impacts supernova dynamics modeling.

Contribution

It introduces a new method to diagnose ELN crossings in 3D CCSN models and demonstrates that fast flavor conversion occurs more in explosive supernovae, highlighting its importance in realistic simulations.

Findings

Fast flavor conversion occurs mainly in the post-shock region.

Explosive models favor conditions for flavor conversion.

ELN crossings are driven by PNS convection and asymmetric neutrino emission.

Abstract

Fast-pairwise collective neutrino oscillation represents a key uncertainty in the theory of core-collapse supernova (CCSN). Despite the potentially significant impact on CCSN dynamics, it is usually neglected in numerical models of CCSN because of the formidable technical difficulties of self-consistently incorporating this physics. In this paper, we investigate the prospects for the occurrence of fast flavor conversion by diagnosing electron neutrino lepton number (ELN) crossing in more than a dozen state-of-the-art three-dimensional CCSN models. ELN crossings is a necessary condition for triggering flavor conversion. Although only zeroth and first angular moments are available from the simulations, our new method enables us to look into the angular distributions of neutrinos in momentum space and provide accurate insight into ELN crossings. Our analysis suggests that fast flavor conversion generally occurs in the post-shock region of CCSNe, and that explosive models provide more favorable conditions for the flavor conversion than failed CCSNe. We also find that there are both common and progenitor-dependent characteristics. Classifying ELN crossings into two types, we analyze the generation mechanism of each case by scrutinizing the neutrino radiation field and matter interactions. We find key ingredients of CCSN dynamics driving the ELN crossings: proto-neutron star (PNS) convection, asymmetric neutrino emission, neutrino absorptions and scatterings. This study suggests that we need to accommodate fast flavor conversions in realistic CCSN models.