Triggering collective oscillations by three-flavor effects
Abstract
Collective flavor transformations in supernovae, caused by neutrino-neutrino interactions, are essentially a two-flavor phenomenon driven by the atmospheric mass difference and the small mixing angle theta13. In the two-flavor approximation, the initial evolution depends logarithmically on theta13 and the system remains trapped in an unstable fixed point for theta13 = 0. However, any effect breaking exact numu-nutau equivalence triggers the conversion. Such three-flavor perturbations include radiative corrections to weak interactions, small differences between the numu and nutau fluxes, or non-standard interactions. Therefore, extremely small values of theta13 are in practice equivalent, the fate of the system depending only on the neutrino spectra and their mass ordering.