  In 2006, a simple extension of the Standard Model was proposed in which
neutrinos obtain radiative Majorana masses at one-loop level from their
couplings with dark matter, hence the term "scotogenic," from the Greek
"scotos" meaning darkness. Here an analogous mechanism for Dirac neutrino
masses is discussed in a minimal model. In different ranges of the parameter
space, various candidates for dark matter are possible. In particular, the
lightest Dirac fermion which appears in the loop diagram generating neutrino
mass can be a viable dark matter candidate. Such a possibility does not exist
for the Majorana case. Realistic neutrino mixing in the context of $A_4$ is
discussed. A possible supersymmetric extension is also briefly discussed.
