Scale of SU(2)R symmetry breaking and leptogenesis

Models of leptogenesis often invoke the out-of-equilibrium decays of heavy right-handed neutrinos in order to create a baryon asymmetry of the universe through the electroweak phase transition. Their presumed existence argues strongly for the presence of an SU(2)R gauge symmetry. We study the equilibrating effects of the resulting additional right-handed interactions and find that successful leptogenesis requires that mN≳1016 GeV if mN>mWR, and mWR≳2×105 GeV(mN/102 GeV)3/4 if mNmWR. We show also that the mN>mWR option is excluded in a supersymmetric theory with gravitinos.