Role of dense matter in collective supernova neutrino transformations
Abstract
For neutrinos streaming from a supernova (SN) core, dense matter suppresses self-induced flavor transformations if the electron density ne significantly exceeds the neutrino density nnu in the conversion region. If ne is comparable to nnu one finds multi-angle decoherence, whereas the standard self-induced transformation behavior requires that in the transformation region nnu is safely above ne. 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.
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