Abstract
We make a simple observation that if one of the right-chiral neutrinos is very heavy or its Yukawa couplings to the standard lepton doublets are negligible, so that it effectively decouples from the see-saw mechanism, the prediction for the baryon asymmetry of the universe resulting from leptogenesis depends only on the masses M1 and M2 of the remaining two right-chiral neutrinos and the element Ỹν22 of the neutrino Yukawa coupling. For M2≳5M1 the lower bound on M1 and also on Treh, resulting from the requirement of ‘successful leptogenesis’ is then significantly increased compared to the one computed recently by Buchmüller et al. in the most general case. Within the framework of thermal leptogenesis, the only way to lower this limit is then to allow for sufficiently small mass difference M2−M1.
Highlights
Accumulated over the past years data on solar and atmospheric neutrino oscillations are consistent with the minimal see-saw mechanism of neutrino mass generation
The differences (1) can result from different patterns of neutrino masses mνi satisfying the WMAP bound1 i mνi < 0.7 eV [1], but the most natural in the context of the see-saw mechanism [2] operating at some scale M close to the GUT scale ∼ 2 × 1016 GeV seems to be the hierarchical pattern mν3 ∼> ∆m2atm, mν2 ∼> ∆m2sol, for which the mixing pattern is stable with respect to radiative corrections [3]
Another attractive feature of the see-saw mechanism is the possibility of explaining the baryon number B asymmetry of the Universe by the out of equilibrium lepton number L violating decays of the right-chiral neutrinos [4]
Summary
Accumulated over the past years data on solar and atmospheric neutrino oscillations are consistent with the minimal see-saw mechanism of neutrino mass generation. Another attractive feature of the see-saw mechanism is the possibility of explaining the baryon number B asymmetry of the Universe by the out of equilibrium lepton number L violating decays of the right-chiral neutrinos [4].
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