Quantum closures for neutrino moment transport

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. As with any moment-based radiation transport method, a closure is needed to suitably truncate the infinite tower of quantum moment evolution equations. The flavor matrix structure of quantum neutrino moments requires the development of genuine "quantum" closures, a relatively uncharted territory.

I will present our recent progress on the theory of quantum closures, focusing on how different closure choices are able to describe the occurrence of fast flavor instabilities (FFIs) in dense environments like neutron star mergers. To that end, we use our previously derived moment-based linear stability analysis, which allows to easily change the closure prescription. In particular, the depth of the angular crossing between (anti)neutrino distributions, at the origin of FFIs, appears to be of prime importance when one seeks to determine how critical the closure choice is in order to match the multi-angle results. This work paves the way to setting prescriptions for quantum closures adapted to neutrino transport in a range of scenarios.