Stability and leptogenesis in the left-right symmetric seesaw mechanism
  We analyze the left-right symmetric type I+II seesaw mechanism, where an eight-fold degeneracy among the mass matrices of heavy right-handed neutrinos M_R is known to exist. Using the stability property of the solutions and their ability to lead to successful baryogenesis via leptogenesis as additional criteria, we discriminate among these eight solutions and partially lift their eight-fold degeneracy. In particular, we find that viable leptogenesis is generically possible for four out of the eight solutions. 
E. K. Akhmedov, M. Blennow, T. Hallgren, T. Konstandin, and T. Ohlsson