Title: Flavour composition and entropy increase of cosmological neutrinos after decoherence,
Abstract: 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.