Radiative seesaw model: Warm dark matter, collider signatures, and lepton flavor violating signals

Extending the standard model with three right-handed neutrinos (Nk) and a second Higgs doublet (η), odd under the discrete parity symmetry Z2, Majorana neutrino masses can be generated at one-loop order. In the resulting model, the lightest stable particle, either a boson or a fermion, might be a dark matter candidate. Here we assume a specific mass spectrum (M1<<M2<M3<mη) and derive its consequences for dark matter and collider phenomenology. We show that (i) the lightest right-handed neutrino is a warm dark matter particle that can give a ∼10% contribution to the dark matter density; (ii) several decay branching ratios of the charged scalar can be predicted from measured neutrino data. Especially interesting is that large lepton flavor violating rates in muon and tau final states are expected. Finally, we derive upper bounds on the right-handed neutrino Yukawa couplings from the current experimental limit on Br(μ→eγ).