Leptogenesis, neutrino mixing data and the absolute neutrino mass scale

Abstract

Recent developments in thermal leptogenesis are reviewed. Neutrino mixing data favor a simple picture where the matter-anti matter asymmetry is generated by the decays of the heavy RH neutrinos mildly close to thermal equilibrium and, remarkably, in the full non relativistic regime. This results into predictions of the final baryon asymmetry not depending on the initial conditions and with minimized theoretical uncertainties. After a short outline of a geometrical derivation of the CP asymmetry bound, we derive analytic bounds on the lightest RH neutrino mass and on the absolute neutrino mass scale. Neutrino masses larger than 0.1 eV are not compatible with the minimal leptogenesis scenario. We discuss how the results get just slightly modified within the minimal supersymmetric standard model. In particular a conservative lower bound on the reheating temperature, T_R \gtrsim 10^9 GeV, is obtained in the relevant effective neutrino mass range tilde{m}_1 \gtrsim 3x10^{-3} eV. We also comment on the existence of a `too-short-blanket problem' in connection with the possibility of evading the leptogenesis neutrino mass bound.