Gravitino constraints on models of neutrino masses and leptogenesis

In the supersymmetric extensions of the standard model, neutrino masses and leptogenesis require the existence of new particles. We point out that if these particles with lepton number violating interactions have standard model gauge interactions, then they may not be created after reheating because of the gravitino problem. This will rule out all existing models of neutrino masses and leptogenesis, except the one with right-handed singlet neutrinos. [S0556-2821(99)05415-6].