Leptogenesis from anÑ-dominated early universe

We investigate in detail leptogenesis by the decay of a coherent right-handed sneutrino $\~N$ having dominated the energy density of the early universe, which was originally proposed by two of the authors (H.M. and T.Y.). Once the $\~N$ dominant universe is realized, the amount of generated lepton asymmetry (and hence baryon asymmetry) is determined only by the properties of the right-handed neutrino, regardless of the history before it dominates the universe. Moreover, thanks to the entropy production by the decay of the right-handed sneutrino, thermally produced relics are sufficiently diluted. In particular, the cosmological gravitino problem can be avoided even when the reheating temperature of inflation is higher than 10¹⁰GeV, in a wide range of the gravitino mass m3/210MeV--100TeV. If the gravitino mass is in the range m3/210MeV--1GeV as in some gauge-mediated supersymmetry breaking models, the dark matter in our Universe can be dominantly composed of the gravitino. The quantum fluctuation of $\~N$ during inflation causes an isocurvature fluctuation which may be detectable in the future.