Inspecting neutrino flavor instabilities during proto-neutron star cooling phase in supernova: I. Spherically symmetric model

TL;DR

This study investigates neutrino flavor instabilities during the cooling phase of proto-neutron stars in supernovae using a spherically symmetric model, finding no flavor conversions but discussing potential effects of multi-dimensional phenomena.

Contribution

It provides a detailed analysis of neutrino flavor stability during PNS cooling with a long-term spherically symmetric model, including Monte Carlo transport for accurate angular distributions.

Findings

No signs of flavor conversions in the models

Flavor stability may change with multi-dimensional effects

Long-term evolution of PNS analyzed with neutrino feedback

Abstract

In the standard model of core-collapse supernova (CCSN), all neutrinos are assumed to be in pure flavor eigenstates in CCSN cores, but the assumption becomes invalid if neutrino distributions are unstable to flavor conversions. In this paper, we present a study of the occurrences of two representative neutrino-flavor instabilities, fast- and collisional flavor instabilities, in the cooling phase of proto-neutron star (PNS) from 1- to 50 seconds. We follow the long-term evolution of a PNS under spherically symmetric and quasi-static approximations, in which the matter profile is determined by solving the Tolman-Oppenheimer-Volkoff equation with neutrino feedback under the treatment of multi-group flux limited diffusion. For the stability analysis of neutrino flavor conversions, we recompute neutrino distributions using Monte Carlo transport in order to obtain the full angular distribution needed to compute the dispersion relations. We find no signs of flavor conversions in our models; the physical reason is thoroughly investigated. We also argue that the negative conclusion in flavor conversions could be changed qualitatively if multi-dimensional effects are included, as similar to cases in the earlier phase of CCSN.