The importance of flavor in leptogenesis

We study leptogenesis from the out-of-equilibrium decays of the lightest heavy neutrino N-1 in the medium (low) temperature regime, T less than or similar to 10(12) GeV (10(9) GeV), where the rates of processes mediated by the tau (and mu) Yukawa coupling are non negligible, implying that the effects of lepton flavors must be taken into account. We find important quantitative and qualitative differences with respect to the case where flavor effects are ignored: (i) The cosmic baryon asymmetry can be enhanced by up to one order of magnitude; (ii) The sign of the asymmetry can be opposite to what one would predict from the sign of the total lepton asymmetry epsilon(1); (iii) Successful leptogenesis is possible even with epsilon(1) = 0.