  Neutrino flavor conversion studies based on astrophysical environments
usually implement neutrino mixings, neutrino interactions with matter and
neutrino self-interactions. In anisotropic media, the most general mean-field
treatment includes neutrino mass contributions as well, that introduce a
coupling between neutrinos and antineutrinos termed helicity or spin coherence.
We discuss resonance conditions for helicity coherence for Dirac and Majorana
neutrinos. We explore the role of these mean-field contributions on flavor
evolution in the context of a binary neutron star merger remnant. We find that
resonance conditions can be satisfied in neutron star merger scenarios while
adiabaticity is not sufficient for efficient flavor conversion. We analyse our
numerical findings by discussing general conditions to have multiple MSW-like
resonances, in presence of non-linear feedback, in astrophysical environments.
