New Developments in Flavor Evolution of a Dense Neutrino Gas

Neutrino-neutrino refraction dominates the flavor evolution in core-collapse supernovae, neutron-star mergers, and early universe. Ordinary neutrino conversion develops on timescales determined by vacuum oscillation frequency. However, when density is large enough, collective may arise because of pairwise scattering. Pairwise deemed to be fast as it expected occur that depend neutrino-neutrino interaction energy (i.e., number density) regulated angular distributions electron neutrinos antineutrinos. The enigmatic phenomenon has been overlooked for a long time. rate, possibly proximity decoupling region with yet understood implications hydrodynamics astrophysical sources synthesis heavy elements. We review physics this fascinating its neutrino-dense sources.