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 cosmological consequences and in particular may be helpful in reconciling Primordial Nucleosynthesis with a high baryon density as suggested by the most recent observations of the Cosmic Microwave Background Radiation. By solving numerically the Boltzmann kinetic equations for the neutrino distribution functions, we find the momentum-dependent corrections to the equilibrium spectra and briefly discuss their phenomenological implications.
Bibliographical noteFunding Information:
The authors thank Alexander Dolgov for fruitful discussions and encouragement. S.P. was supported by the TMR network grant ERBFMRXCT960090. S.P. and M.P. were supported by I.N.F.N.
- Early Universe
- Lepton asymmetry
- Non-equilibrium kinetics