Non equilibrium spectra of degenerate relic neutrinos

We calculate the exact kinetic evolution of cosmic neutrinos until complete decoupling, in the case when a large neutrino asymmetry exists. While not excluded by present observations, this large asymmetry can have relevant co smological consequences and in particular may be helpful in reconciling Pri mordial Nucleosynthesis with a high baryon density as suggested by the most recent observations of the Cosmic Microwave Background Radiation. By solvi ng numerically the Boltzmann kinetic equations for the neutrino distributio n functions, we find the momentum-dependent corrections to the equilibrium spectra and briefly discuss their phenomenological implications. (C) 2000 E lsevier Science B.V, All rights reserved.