  We discuss the connection between the origin of neutrino masses and the
properties of dark matter candidates in the context of gauge extensions of the
Standard Model. We investigate minimal gauge theories for neutrino masses where
the neutrinos are predicted to be Dirac or Majorana fermions. We find that the
upper bound on the effective number of relativistic species provides a strong
constraint in the scenarios with Dirac neutrinos. In the context of theories
where the lepton number is a local gauge symmetry spontaneously broken at the
low scale, the existence of dark matter is predicted from the condition of
anomaly cancellation. Applying the cosmological bound on the dark matter relic
density, we find an upper bound on the symmetry breaking scale in the multi-TeV
region. These results imply we could hope to test simple gauge theories for
neutrino masses at current or future experiments.
