Quantum Coherence of Relic Neutrinos

The cosmic neutrino background (i.e., the relic neutrinos) last scattered in the early universe when the photon-baryon plasma was very hot, around the epoch of big bang nucleosynthesis. At this last scattering surface the neutrinos are largely in flavor eigenstates. We discuss the implications of this fact on cosmology and cosmological limits on neutrino parameters.