PUB - Publikationen an der Universität Bielefeld

We investigate the evolution of the flavour composition of the cosmic neutrino background from neutrino decoupling until today. The decoherence of neutrino mass states is described by means of Lindblad operators. Decoherence goes along with the increase of neutrino family entropy, which we obtain as a function of initial spectral distortions, mixing angles and CP-violation phase. We also present the expected flavour composition of the cosmic neutrino background after decoherence is completed. Decoherence is proposed to happen after the two heaviest neutrino mass states become non-relativistic. We discuss how the associated increase of entropy could be observed (in principle). The physics of two- or three-flavour oscillation of cosmological neutrinos resembles in many aspects two- or three-level systems in atomic clocks, which were recently proposed by Weinberg for the study of decoherence phenomena.