Electroweak Baryogenesis and Constraints on Left-handed Majorana   Neutrino Masses
  The lepton number violating interactions generated by the light Majorana neutrinos can erase the primordial baryon asymmetry of the universe during the electroweak phase transition. The Majorana masses of the left-handed neutrinos are constrained to avoid this problem. These constraints do not depend on the $(B-L)$ symmetry breaking mechanism. 
Utpal Sarkar