In the dense supernova core, self-interactions may align the flavor polarization vectors of $\nu$ and $\overline{\nu }$ and induce collective flavor transformations. Different alignment Ansätze are known to describe approximately the phenomena of synchronized or bipolar oscillations and the split of $\nu$ energy spectra. We discuss another phenomenon observed in some numerical experiments in inverted hierarchy, showing features akin to a low-energy split of $\overline{\nu }$ spectra. The phenomenon appears to be approximately described by another alignment Ansatz which, in the considered scenario, reduces the (nonadiabatic) dynamics of all energy modes to only two $\nu$ plus two $\overline{\nu }$ modes. The associated spectral features, however, appear to be fragile when passing from single to multiangle simulations.

• Received 7 August 2008

DOI:https://doi.org/10.1103/PhysRevD.78.097301