Core-collapse supernovae: When neutrinos Get to Know each other

When the neutrino density is very high, as in core-collapse supernovae, neutrino-neutrino forward scattering many appreciable affect the evolution of flavor. In a sense, neutrinos 'get to know each other' and behave in a collective (rather than individual) way. This phenomenon is briefly highlighted within 2ν and 3ν frameworks, with emphasis on split/swap features observable in energy spectra from future galactic supernova. Detection of such effects could provide a handle on two unknowns: the neutrino mass hierarchy and the mixing angle θ13.