The neutrino magnetic moment and supernovae with strong magnetic fields

Despite several decades of searches, the neutrino magnetic moment remains unknown. If it is large, the neutrino evolution can be affected by its coupling to strong magnetic fields like the ones present in at least some core-collapse supernovae. We explore these effects for Majorana neutrinos. We first discuss a schematic model often employed and show the impact of resonant spin-flavor precession on the neutrino signal for a future galactic supernova. Then, we consider detailed simulations of a neutrino-driven supernova with 17 ${\mathrm{M}}_{\odot }$ leaving a neutron star and a magnetorotational supernova with 26 ${\mathrm{M}}_{\odot }$ with a black-hole remnant. We present predictions for the supernova neutrino fluxes and the event rates in presence of a non-zero neutrino magnetic moment, for the running JUNO and upcoming Hyper-Kamiokande experiments. Our results show a significant impact for transition magnetic moments of ${10}^{-14}{\mu }_B$ during the neutronization burst and the accretion phase for the neutrino driven supernova, and as small as ${10}^{-15}{\mu }_B$ at the early times for the magnetorotational supernova.