Fast Neutrino Flavor Conversion Modes in Multidimensional Core-collapse Supernova Models: the Role of the Asymmetric Neutrino Distributions

TL;DR

This study investigates fast neutrino flavor conversions in supernova models, revealing how angular distributions and multipole components influence the occurrence of flavor crossings in different progenitor scenarios.

Contribution

It provides a detailed analysis of neutrino angular distributions in multidimensional supernova models, linking angular crossings to multipole components and progenitor characteristics.

Findings

Angular crossings occur in the 11.2 M_sun model but not in the 27 M_sun model.

Higher multipole components increase the likelihood of angular crossings.

Multiple crossings can exist between neutrino angular distributions.

Abstract

A dense neutrino gas, such as the one anticipated in the supernova environment, can experience fast neutrino flavor conversions on scales much shorter than those expected in vacuum probably provided that the angular distributions of $\nu_e$ and $\bar\nu_e$ cross each other. We perform a detailed investigation of the neutrino angular distributions obtained by solving the Boltzmann equations for fixed matter profiles of some representative snapshots during the post-bounce phase of core-collapse supernovae in multidimensional calculations of an $11.2\mathrm{M}_{\odot}$ and a $27\mathrm{M}_{\odot}$ progenitor models. Although the $11.2\mathrm{M}_{\odot}$ model features $\nu_e - \bar\nu_e$ angular crossings and the associated fast modes at different time snapshots, the $27\mathrm{M}_{\odot}$ model does not show any crossings within the decoupling region. We show that this can be understood by studying the multipole components of the neutrino distributions. In fact, there is a higher chance for the occurrence of $\nu_e - \bar\nu_e$ angular crossings for the zones where the multipole components of the neutrino distributions are strong enough. We also show that there can exist more than one crossings between the angular distributions of $\nu_e$ and $\bar{\nu}_e$. In addition, apart from the crossings within the neutrino decoupling region, there is a class of $\nu_e-\bar\nu_e$ angular crossings which appears very deep inside the proto-neutron star.