Neutrino quantum kinetics in a core-collapse supernova

TL;DR

This paper presents detailed simulations of neutrino flavor conversion in a supernova core, revealing how flavor dynamics evolve over time and impact supernova physics.

Contribution

It introduces multi-angle, multi-energy quantum kinetic simulations of neutrinos near the decoupling region, highlighting the time-dependent emergence of flavor conversions.

Findings

No flavor crossing at early times ($t_{pb} \,\lesssim\, 0.5$ s)

Fast flavor conversion leads to flavor equipartition at later times

Flavor equipartition depends on neutrino properties during late accretion phase

Abstract

Our understanding of neutrino flavor conversion in the supernova core is still preliminary, despite its likely relevance to the neutrino-driven supernova mechanism. We present multi-angle and multi-energy numerical simulations of neutrino quantum kinetics within a spherically symmetric shell in the proximity of the region of neutrino decoupling. We rely on inputs from a one-dimensional core-collapse supernova model with a mass of $18.6\ M_\odot$ and find that, at early post-bounce times ($t_{\mathrm pb} \lesssim 0.5$~s), no crossing is present in the angular distribution of the electron neutrino lepton number and flavor conversion is triggered by slow collective instabilities. Angular crossings appear for $t_{\textrm{pb}} \gtrsim 0.5$~s and fast flavor conversion leads to flavor equipartition, with the spectral energy distribution of $\nu_{e}$ ($\bar{\nu}_{e}$) and $\nu_{x}$ ($\bar{\nu}_{x}$) becoming comparable. Notably, flavor equipartition is not a generic outcome of fast flavor conversion, rather it is a consequence of the relatively similar properties of neutrinos of different flavors characterizing the late accretion phase. Artificially tweaking the collision term to introduce an electron lepton number angular crossing for $t_{\mathrm{pb}} \lesssim 0.05$~s, we observe that flavor equipartition is not achieved. While our findings are restricted to a specific supernova model, and they only take into account the feedback of the neutrino background on the flavor conversion, they suggest a rich phenomenology in the supernova core as a function of the post-bounce time which needs to be further explored to assess its impact on the explosion mechanism.