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Neutrino oscillations in the early universe: How large lepton asymmetry can be generated?

A. D. Dolgov, S. H. Hansen, S. Pastor, D. V. Semikoz

hep-pharXiv:hep-ph/9910444

Abstract

The lepton asymmetry that could be generated in the early universe through oscillations of active to sterile neutrinos is calculated (almost) analytically for small mixing angles, sin 2θ< 10-2. It is shown that for a mass squared difference, δm2=-1 eV2 it may rise at most by 6 orders of magnitude from the initial ``normal'' value of 10-10, since the back-reaction from the refraction index terminates this rise while the asymmetry is still small. Only for very large mass differences, δm2 about 109 eV2, the lepton asymmetry could reach a significant magnitude exceeding 0.1.

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