Neutrino flavor mixing with moments

Abstract

The successful transition from core-collapse supernova simulations using classical neutrino transport to simulations using quantum neutrino transport will require the development of methods for calculating neutrino flavor transformations that mitigate the computational expense. One potential approach is the use of angular moments of the neutrino field, which has the added appeal that there already exist simulation codes which make use of moments for classical neutrino transport. Evolution equations for quantum moments based on the quantum kinetic equations can be straightforwardly generalized from the evolution of classical moments based on the Boltzmann equation. We present an efficient implementation of neutrino transformation using quantum angular moments in the free streaming, spherically symmetric bulb model. We compare the results against analytic solutions and the results from more exact multi-angle neutrino flavor evolution calculations. We find that our moment-based methods employing scalar closures predict, with good accuracy, the onset of collective flavor transformations seen in the multi-angle results. However, they over-estimate the coherence between neutrinos traveling along different trajectories in tests that neglect neutrinoneutrino interactions. More sophisticated quantum closures may improve the agreement between the inexpensive moment-based methods and the multi-angle approach.

Fast neutrino conversion in hydrodynamic simulations of neutrino-cooled accretion disks

“…Apart from the, already significant, uncertainties connected to neutrino transport that assumes massless neutrinos, additional, major questions are connected to the possibility that finite-mass neutrinos could change their flavor during the propagation through and out of the disk. An immediate consequence of flavor conversion, e.g., due to neutrino self-interactions, is that the change in the abundances and mean energies of ν e and νe neutrinos would lead to a modified value of the equilibrium electron fraction corresponding to neutrino absorption, Y eq;abs e [38,54], as well as the timescale over which Y e approaches Y eq;abs e in outflows exposed to neutrino irradiation [55][56][57][58][59][60][61][62][63][64][65][66]. In a dense neutrino gas, such as the one expected in the innermost regions of neutrino-cooled disks, neutrinos could also experience fast flavor conversion [67,68] (see also [69,70] and references therein).…”

Neutrino Flavor Conversions in High-Density Astrophysical and Cosmological Environments

“…A more realistic approach can be either moving away from flavor equilibration, or writing Equation (2) in terms of the angular and energy moments of the density matrix p,x . The latter possibility is numerically more manageable and it has been recently adopted [265]. Finally, we underline the importance of cross checks between different numerical codes.…”

Neutrino Fast Flavor Instability in three dimensions for a Neutron Star Merger

“…Note that the the evolution equations in spherical coordinates [89] are slightly different with an additional, 'geometrical source' term on the lhs.…”