Dirac neutrinos in the seesaw mechanism. Dirac lepton number violation

Abstract: The seesaw mechanism explains the exclusive smallness of neutrino masses by the presence of very heavy Majorana masses and leads to the appearance of Majorana particles and to the direct lepton number violation. The author proposes a seesaw scenario that produces only Dirac neutrinos with the same violation. This scenario appears possible for heavy neutrinos with non-perturbative Higgs boson H couplings. Such a scenario could be accomplished in the model describing the structure of weak mixing matrices for quarks and leptons through the existence of very heavy mirror analogs of Standard Model fermions. The non-perturbativity of the problem hinders the analytical solution, but the conditions derived indicate that the mechanism under consideration preferentially generates only Dirac neutrinos. This phenomenon may have relevance for leptogenesis processes if all existing neutrinos turn out to be of the Dirac type.