A model of electroweak-scale right-handed neutrino mass

If neutrino masses are realized through the see-saw mechanism, can the right-handed neutrinos be produced and detected at present and future colliders? The answer is negative in the most popular see-saw scenarios for the simple reason that they are too heavy in these models. However, a simple extension of the Standard Model (SM) particle content, including mirror fermions, two SU(2)L triplet and one singlet Higgs fields, leads to a scenario in which the see-saw mechanism is realized with the Majorana mass MR of the right-handed neutrino being of the order of the electroweak scale or smaller. A custodial SU(2) symmetry arising from the two triplet Higgs fields ensures that ρ=1 at tree level even when their vacuum expectation values (VEV) which determine the value of MR, can be as large as the electroweak scale. MR is found to obey the bound MZ2⩽MR<246GeV which makes it accessible experimentally (Tevatron, LHC or ILC) since, in our scenario, νR's can couple directly to the Standard Model (SM) gauge bosons.