A simple connection between neutrino oscillation and leptogenesis

The usual see-saw formula is modied by the presence of two Higgs tripletsinleft-rightsymmetrictheories. Thecontributionfromtheleft-handedHiggs triplet to the see-saw formula can dominate over the conventional one when the neutrino Dirac mass matrix is identied with the charged lepton or down quark massmatrix. Inthiscaseananalyticcalculationoftheleptonasymmetry,generated by the decay ofthelightest right-handed Majorananeutrino, ispossible. Fortypical parameters, the out-of-equilibrium condition for the decay is automatically fullled. The baryon asymmetry has the correct order of magnitude, as long as the lightest mass eigenstate is not much lighter then 10 6 to 10 8 eV, depending on the solution ofthesolarneutrino problem. Asizablesignalinneutrinoless doublebetadecaycan beexpected,aslongasthesmallestmasseigenstateisnotmuchlighterthan10 3 eV and the Dirac mass matrix is identied with the charged lepton mass matrix.