Non equilibrium spectra of degenerate relic neutrinos

We calculate the exact kinetic evolution of cosmic neutrinos during the epoch previous to Big Bang Nucleosynthesis, in the case when a large neutrino asymmetry exists. By solving numerically the Boltzmann kinetic equations for the neutrino distribution functions, we find the momentum-dependent corrections to the equilibrium spectrum of neutrinos and discuss their phenomenological implications. Motived by recent observations of the Cosmic Microwave Background Radiation, which seem to favour a larger baryon content in the Universe than that required by standard Nucleosynthesis, we also update the Nucleosynthesis bounds on neutrino chemical potentials.