Role of dense matter in collective supernova neutrino transformations

TL;DR

This paper explores how dense matter influences collective neutrino flavor transformations in supernovae, revealing conditions under which matter suppresses or allows these transformations, especially considering multi-angle effects from non-point-like sources.

Contribution

It introduces a new multi-angle effect showing how neutrino trajectories affect flavor transformations in dense matter environments.

Findings

Dense matter suppresses flavor transformations when electron density exceeds neutrino density.

Multi-angle decoherence occurs when electron and neutrino densities are comparable.

Neutrino trajectories from extended sources lead to subtle multi-angle effects.

Abstract

For neutrinos streaming from a supernova (SN) core, dense matter suppresses self-induced flavor transformations if the electron density n_e significantly exceeds the neutrino density n_nu in the conversion region. If n_e is comparable to n_nu one finds multi-angle decoherence, whereas the standard self-induced transformation behavior requires that in the transformation region n_nu is safely above n_e. This condition need not be satisfied in the early phase after supernova core bounce. Our new multi-angle effect is a subtle consequence of neutrinos traveling on different trajectories when streaming from a source that is not point-like.