3-Dimensional, Multi-Flavor Neutrino Spin Oscillations In the Presence of a Fast Flavor Instability

In the presence of anisotropic neutrino and antineutrino fluxes, the neutrino quantum kinetic equations acquire helicity off-diagonal terms that drive coherent oscillations in neutrino spin. These oscillations depend directly on the absolute mass scale and Majorana phase, but are usually too transient to produce important effects. In this paper we present a 3-dimensional analysis of spin oscillations, analyzing the effect on the data of the 3D neutron star merger of cite{merger_simulation}. We find an interesting directional dependence that allows for resonant { ed and significant} oscillations to occur along specific directions. The solid angle spanned by these directions is extremely narrow in general, but we propose conditions under which it could be broadened. We then analyze spin-flip in the mixed-flavor regime by characterizing how the effect's resonance and timescale change during a fast flavor instability. For this analysis, we derive a generalized resonance condition that poses a restrictive requirement for resonance to exist in any flavor channel.