Decoherence in supernova neutrino transformations suppressed by deleptonization

TL;DR

This paper investigates how deleptonization flux influences flavor decoherence in supernova neutrinos, finding that sufficient deleptonization suppresses multi-angle decoherence, especially under typical supernova conditions.

Contribution

It identifies the critical role of deleptonization flux in suppressing multi-angle flavor decoherence in supernova neutrinos, providing a quantitative threshold.

Findings

Multi-angle decoherence is suppressed for epsilon > 0.3.

Normal hierarchy and small mixing angles require less asymmetry for suppression.

Deleptonization flux likely prevents decoherence in realistic supernova scenarios.

Abstract

In the dense-neutrino region at 50-400 km above the neutrino sphere in a supernova, neutrino-neutrino interactions cause large flavor transformations. We study when the multi-angle nature of the neutrino trajectories leads to flavor decoherence between different angular modes. We consider a two-flavor mixing scenario between nu_e and another flavor nu_x and assume the usual hierarchy F(nu_e)>F{antinu_e)>F(nu_x)=F(antinu_x) for the number fluxes. We define epsilon=(F(nu_e)-F(antinu_e))/(F(antinu_e)-F(antinu_x)) as a measure for the deleptonization flux which is the one crucial parameter. The transition between the quasi single-angle behavior and multi-angle decoherence is abrupt as a function of epsilon. For typical choices of other parameters, multi-angle decoherence is suppressed for epsilon>0.3, but a much smaller asymmetry suffices if the neutrino mass hierarchy is normal and the mixing angle small. The critical epsilon depends logarithmically on the neutrino luminosity. In a realistic supernova scenario, the deleptonization flux is probably enough to suppress multi-angle decoherence.