Quantum Closures for Neutrino Moment Transport

TL;DR

This paper introduces a new quantum closure parameterization for neutrino flavor transport using angular moments, enabling efficient simulations that can replicate multi-angle results.

Contribution

It develops a general quantum closure parameterization for neutrino moment transport and demonstrates its effectiveness in reproducing detailed multi-angle calculations.

Findings

The parameterization satisfies physical constraints.

It accurately reproduces multi-angle results in test cases.

It enables efficient neutrino flavor transport simulations.

Abstract

A computationally efficient method for calculating the transport of neutrino flavor in simulations is to use angular moments of the neutrino one-body reduced density matrix, i.e., `quantum moments'. As with any moment-based radiation transport method, a closure is needed if the infinite tower of moment evolution equations is truncated. We derive a general parameterization of a quantum closure and the limits the parameters must satisfy in order for the closure to be physical. We then derive from multi-angle calculations the evolution of the closure parameters in two test cases which we then progressively insert into a moment evolution code and show how the parameters affect the moment results until the full multi-angle results are reproduced. This parameterization paves the way to setting prescriptions for genuine quantum closures adapted to neutrino transport in a range of situations.