  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.
