Quantum maximum entropy closure for small flavor coherence

TL;DR

This paper introduces a novel quantum M1 closure relation based on maximum entropy principles, specifically for small flavor coherence, improving the modeling of neutrino flavor mixing in dense astrophysical environments.

Contribution

It provides the first analytic quantum M1 closure for small flavor coherence, validated in different regimes, and demonstrates improved stability analysis in neutron star merger simulations.

Findings

Closure relation has correct limits and speeds in different regimes

Enhanced detection of fast flavor instabilities in simulations

Outperforms previous ad hoc semiclassical closures

Abstract

Quantum angular moment transport schemes are an important avenue toward describing neutrino flavor mixing phenomena in dense astrophysical environments such as supernovae and merging neutron stars. Successful implementation will require new closure relations that go beyond those used in classical transport. In this paper, we derive the first analytic expression for a quantum M1 closure, valid in the limit of small flavor coherence, based on the maximum entropy principle. We verify that the resulting closure relation has the appropriate limits and characteristic speeds in the diffusive and free-streaming regimes. We then use this new closure in a moment linear stability analysis to search for fast flavor instabilities in a binary neutron star merger simulation and find better results as compared with previously designed, ad hoc, semiclassical closures.