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

TL;DR

This paper investigates low-energy spectral features of supernova (anti)neutrinos in inverted hierarchy, revealing a fragile spectral split phenomenon linked to specific flavor alignment scenarios.

Contribution

It introduces a new alignment ansatz that simplifies the flavor transformation dynamics and explains low-energy spectral splits in supernova neutrinos.

Findings

Spectral split phenomena are observed in inverted hierarchy.

The new ansatz reduces complex dynamics to a two-neutrino plus two-antineutrino mode model.

Spectral features are fragile in multi-angle simulations.

Abstract

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