Systematic Study of One-Loop Dirac Neutrino Masses and Viable Dark Matter Candidates

We study the generation of small neutrino masses from the dimension six effective operator at tree level and one-loop level, the neutrinos are assumed to be Dirac particles. We find out all possible tree and one-loop diagrams which lead to finite neutrino masses. The relevant mediator fields and the predictions for neutrino masses are presented. The lower order contributions to neutrino masses can be forbidden by introducing soft breaking abelian symmetry or finite non-abelian symmetry. The messengers inside the loop can be dark matter particles. The possible dark matter candidates and the corresponding constraints on the parameter $\alpha$ are analyzed for each model.