Relic neutrino asymmetry, CMB and large-scale structure

We consider some consequences of the presence of a cosmological lepton asym metry in the form of neutrinos. A relic neutrino degeneracy enhances the co ntribution of massive neutrinos to the present energy density of the Univer se, and modifies the power spectrum of radiation and matter. Comparing with current observations of cosmic microwave background anisotropies and large scale structure, we derive some constraints on the relic neutrino degenera cy and on the spectral index in the case of a flat Universe with a cosmolog ical constant.