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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 parametrization of a quantum closure and the limits the parameters must satisfy in order for the closure to be physical. We then derive from multiangle 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 multiangle results are reproduced. This parametrization paves the way to setting prescriptions for genuine quantum closures adapted to neutrino transport in a range of situations. Published by the American Physical Society2025
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This content will become publicly available on March 1, 2026
Quantum maximum entropy closure for small flavor coherence
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, , semiclassical closures. Published by the American Physical Society2025
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- Award ID(s):
- 2020275
- PAR ID:
- 10596539
- Publisher / Repository:
- APS
- Date Published:
- Journal Name:
- Physical Review D
- Volume:
- 111
- Issue:
- 6
- ISSN:
- 2470-0010
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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