  Neutrinos streaming from a supernova (SN) core occasionally scatter in the
envelope, producing a small "neutrino halo" with a much broader angle
distribution than the primary flux originating directly from the core. Cherry
et al. (2012) have recently pointed out that, during the accretion phase, the
halo actually dominates neutrino-neutrino refraction at distances exceeding
some 100 km. However, the multiangle matter effect (which increases if the
angle distribution is broader) still appears to suppress self-induced flavor
conversion during the accretion phase.
