Novel TeV-scale seesaw mechanism with Dirac mediators

We propose novel tree level seesaw mechanism with TeV-scale vectorlike Dirac mediators that produce Majorana masses of the known neutrinos. The gauge quantum number assignment to the Dirac mediators allows them to belong to a weak triplet and a five-plet of non-zero hypercharge. The latter leads to new seesaw formula mν∼v6/M5, so that the empirical masses mν∼10−1 eV can be achieved by M∼TeV new states. There is a limited range of the parameter space with M⩽a few100 GeV where the tree level contribution dominates over the respective loop contributions and the proposed mechanism is testable at the LHC. We discuss specific signatures for Dirac type heavy leptons produced by Drell–Yan fusion at the LHC.