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.

• Received 6 July 2012

DOI:https://doi.org/10.1103/PhysRevD.86.033007