Neutrino Mass Hierarchy and Stepwise Spectral Swapping of Supernova Neutrino Flavors

Abstract

We examine a phenomenon recently predicted by numerical simulations of supernova neutrino flavor evolution: the swapping of supernova $ν_e$ and $ν_{μ,τ}$ energy spectra below (above) energy $\EC$ for the normal (inverted) neutrino mass hierarchy. We present the results of large-scale numerical calculations which show that in the normal neutrino mass hierarchy case, $\EC$ decreases as the assumed $ν_e\rightleftharpoonsν_{μ,τ}$ effective $2\times 2$ vacuum mixing angle ($\simeq θ_{1 3}$) is decreased. However, these calculations also indicate that $\EC$ is essentially independent of the vacuum mixing angle in the inverted neutrino mass hierarchy case. With a good neutrino signal from a future Galactic supernova, the above results could be used to determine the neutrino mass hierarchy even if $θ_{13}$ is too small to be detected in terrestrial neutrino oscillation experiments.

4 pages, 2 figures. Version accepted by PRL