Generalized ℤ2 × ℤ2 in scaling neutrino Majorana mass matrix and baryogenesis via flavored leptogenesis

In the seesaw model, the baryon asymmetry of the Universe can be generated by the decay of the lightest right-handed neutrino, nu_R. For a hierarchical spectrum of right-handed neutrinos, we show that there is a model independent upper bound on the CP asymmetry produced in these decays: epsilon ^2). This implies that epsilon and the mass M_{nu_R} of the lightest right-handed neutrino are not independent parameters, as is commonly assumed. If m_{nu_3} = sqrt{Delta m^2_{atm}} and the nu_R are produced thermally, then leptogenesis requires a reheat temperature of the Universe T_{reh} > M_{nu_R} > 10^8 GeV. Reasonable estimates of nu_R production and the subsequent washout of the asymmetry, as made by Buchmuller and Plumacher, imply M_{nu_R} > 10^9 GeV, and T_{reh} > 10^{10} GeV. Implications for the gravitino problem are also discussed.

Leptogenesis is a class of scenarios where the baryon asymmetry of the Universe is produced from a lepton asymmetry generated in the decays of a heavy sterile neutrino. We explain the motivation for leptogenesis. We review the basic mechanism, and describe subclasses of models. We then focus on recent developments in the understanding of leptogenesis: finite temperature effects, spectator processes, and in particular the significance of flavor physics.