Spin-Flavor Precession Phase Effects in Supernova

Abstract: We study the phase effects driven by neutrino magnetic moment for Majorana neutrinos in a core collapse supernova. A neutrino with a large magnetic moment is emitted in a superposition of energy eigenstates from the neutrinosphere. These energy eigenstates can interfere to create a phase effect at a partially adiabatic spin flavor precession (SFP) resonance. We examine the dependence of the SFP phase effect on the size of the neutrino magnetic moment as well as its variation with the post bounce time. In particular, at late post-bounce times the SFP resonance becomes wider and eventually overlaps with the Mikheev-Smirnov-Wolfenstein (MSW) resonance. At this point, Landau-Zener criteria for adiabaticity can no longer be applied to individual resonances, but we show that SFP phase effect is still present after the overlap. We also discuss the observability of the SFP phase effect at late post bounce times where it is more likely to make an impact. Our analysis for the Deep Underground Neutrino Experiment (DUNE) reveals that at low energies event rates do not fluctuate despite the presence of a sizable SFP phase effect. We find larger event rate fluctuations at high energies, but these fluctuations are also erased in the energy spectra of the observed charged leptons. A more refined treatment of electron fraction and the inclusion of neutrino-neutrino interactions may change our conclusions for observability in future studies.