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 multiangle nature of the neutrino trajectories leads to flavor decoherence between different angular modes. We consider a two-flavor mixing scenario between e and another flavor x and assume the usual hierarchy F e > F e > F x F x for the number fluxes. We define F e ÿ F e =F e ÿ F x as a measure for the deleptonization flux which is the one crucial parameter. The transition between the quasi-single-angle behavior and multiangle decoherence is abrupt as a function of . For typical choices of other parameters, multiangle decoherence is suppressed for * 0:3, but a much smaller asymmetry suffices if the neutrino mass hierarchy is normal and the mixing angle small. The critical depends logarithmically on the neutrino luminosity. In a realistic supernova scenario, the deleptonization flux is probably enough to suppress multiangle decoherence.

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 nν in the conversion region. If ne is comparable to nν one finds multi-angle decoherence, whereas the standard self-induced transformation behavior requires that in the transformation region nν is safely above ne. This condition need not be satisfied in the early phase after SN 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.

We analyze the possibility of probing nonstandard neutrino interactions (NSI, for short) through the detection of neutrinos produced in a future galactic supernova (SN). We consider the effect of NSI on the neutrino propagation through the SN envelope within a three-neutrino framework, paying special attention to the inclusion of NSI-induced resonant conversions, which may take place in the most deleptonized inner layers. We study the possibility of detecting NSI effects in a Megaton water Cherenkov detector, either through modulation effects in the e spectrum due to (i) the passage of shock waves through the SN envelope, (ii) the time dependence of the electron fraction, and (iii) the Earth matter effects; or, finally, through the possible detectability of the neutronization e burst. We find that the e spectrum can exhibit dramatic features due to the internal NSI-induced resonant conversion. This occurs for nonuniversal NSI strengths of a few %, and for very small flavor-changing NSI above a few 10 ÿ5 .

We study three-flavor collective neutrino transformations in the dense-neutrino region above the neutrino sphere of a supernova core. We find that two-flavor conversions driven by the atmospheric mass difference and the 13-mixing angle capture the full effect if one neglects the second-order difference between the and refractive index. Including this ''mu-tau matter term'' provides a resonance at a density of 3 10 7 g cm ÿ3 that typically causes significant modifications of the overall e and e survival probabilities. This effect is surprisingly sensitive to deviations from maximal 23-mixing, being different for each octant.

We consider the effect of non-standard neutrino interactions (NSI, for short) on the propagation of neutrinos through the supernova (SN) envelope within a three-neutrino framework and taking into account the presence of a neutrino background. We find that for given NSI parameters, with strength generically denoted by εij, neutrino evolution exhibits a significant time dependence. For |εττ | 10−3 the neutrino survival probability may become sensitive to the ϑ23 octant and the sign of εττ .In particular, if εττ 10 −2 an internal I-resonance may arise independently of the matter density.For typical values found in SN simulations this takes place in the same dense-neutrino region above the neutrinosphere where collective effects occur, in particular during the synchronization regime.This resonance may lead to an exchange of the neutrino fluxes entering the bipolar regime. The main consequences are (i) bipolar conversion taking place for normal neutrino mass hierarchy and(ii) a transformation of the flux of low-energy νe, instead of the usual spectral swap.