Dirac Neutrinos and Dark Matter Stability from Lepton Quarticity
  We propose to relate dark matter stability to the possible Dirac nature of
neutrinos. The idea is illustrated in a simple scheme where small Dirac
neutrino masses arise from a type--I seesaw mechanism as a result of a $Z_4$
discrete lepton number symmetry. The latter implies the existence of a viable
WIMP dark matter candidate, whose stability arises from the same symmetry which
ensures the Diracness of neutrinos.
