Flavour composition and entropy increase of cosmological neutrinos after
  decoherence
  We propose that gravitational interactions of cosmic neutrinos with the
statistically homogeneous and isotropic fluctuations of space-time leads to
decoherence. This working hypothesis, which we describe by means of a Lindblad
operator, is applied to the system of two- and three-flavour neutrinos
undergoing vacuum oscillations and the consequences are investigated. As result
of this decoherence we find that the neutrino entropy would increase as a
function of initial spectral distortions, mixing angles and CP-violation phase.
Subsequently we discuss the chances to discover such an increase
observationally (in principle). We also present the expected flavour
composition of the cosmic neutrino background after decoherence is completed.
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.
