The importance of flavor in leptogenesis

We study leptogenesis from the out-of-equilibrium decays of the lightestheavy neutrino $N_1$ in the medium (low) temperature regime, $T\lsim 10^{12}$GeV ($10^{10}$ GeV), where the rates of processes mediated by the $\tau$ (and$\mu$) Yukawa coupling are non negligible, implying that the effects of leptonflavors must be taken into account. We find important quantitative andqualitative differences with respect to the case where flavor effects areignored: (i) The cosmic baryon asymmetry can be enhanced by up to one order ofmagnitude; (ii) The sign of the asymmetry can be opposite to what one wouldpredict from the sign of the total lepton asymmetry $\epsilon_1$; (iii)Successful leptogenesis is possible even with $\epsilon_1=0$.Comment: 27 pages, 2 figures. Added 3 reference