We propose a new mechanism where both Dirac masses for the charged leptons and Majorana masses for neutrinos are generated via quantum levels. The charged-lepton masses are given by the vacuum expectation values (VEVs) of the Higgs doublet field and that of a triplet field. On the other hand, neutrino masses are generated by two VEVs of triplet Higgs fields. As a result, the hierarchy between the masses for charged leptons and neutrinos can be explained by the triplet VEVs which have to be much smaller than the doublet VEV due to the constraint from the electroweak rho parameter. We construct a concrete model to realize this mechanism with discrete ${\mathbb{Z}}_2$ and ${\mathbb{Z}}_4$ symmetries, in which masses for neutrinos and those for the muon and electron are generated at the one-loop level. As a bonus in our model, the deviation in the measured muon $g-2$ from the standard model prediction can be explained by contributions of extra particle loops. Besides, the lightest ${\mathbb{Z}}_2$-odd neutral particle can be a dark matter candidate. The collider phenomenology is also discussed, especially focusing on doubly charged scalar bosons which are necessary to introduce to occur our mechanism.

• Received 24 November 2013

DOI:https://doi.org/10.1103/PhysRevD.89.053008