Low-energy spectral features of supernova (anti)neutrinos in inverted hierarchy

In the dense supernova core, self-interactions may align the flavor polarization vectors of v and (v) over bar and induce collective flavor transformations. Different alignment Ansatze are known to describe approximately the phenomena of synchronized or bipolar oscillations and the split of v energy spectra. We discuss another phenomenon observed in some numerical experiments in inverted hierarchy, showing features akin to a low-energy split of (v) over bar 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 v plus two (v) over bar modes. The associated spectral features, however, appear to be fragile when passing from single to multiangle simulations.