We consider some consequences of the presence of a cosmological lepton asymmetry in the form of neutrinos. A relic neutrino degeneracy enhances the contribution of massive neutrinos to the present energy density of the Universe, 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 neutrino degeneracy and on the spectral index in the case of a flat universe with a cosmological constant.

• Received 21 April 1999

DOI:https://doi.org/10.1103/PhysRevD.60.103521