TeV-scale seesaw mechanism with quintuplet fermions

We propose a new seesaw model based on a fermionic hypercharge-zero weak quintuplet in conjunction with an additional scalar quadruplet which attains an induced vacuum expectation value. The model provides both tree-level seesaw similar to upsilon(6)/M-5 and loop-suppressed radiative similar to(1/16 pi(2)) . upsilon(2)/M contributions to active neutrino masses. The empirical masses m(v) similar to 10(-1) eV can be achieved with M similar to TeV new states, accessible at the LHC. For 5 fb(-1) of accumulated integrated luminosity at the LHC, there could be similar to 500 doubly-charged Sigma(++) or (Sigma(++)) over bar fermions with mass M-Sigma = 400 GeV, leading to interesting multilepton signatures. The neutral component of the fermion quintuplet, previously identified as a minimal dark matter candidate, becomes unstable in the proposed seesaw setup. The stability can be restored by introducing a Z(2) symmetry, in which case neutrinos get mass only from radiative contributions.