Probing TeV scale origin of neutrino mass at future lepton colliders via neutral and doubly-charged scalars

Abstract

We point out how future lepton colliders can provide unique insight into the scalar sector of TeV scale models for neutrino masses with local B-L symmetry. Our specific focus is on the TeV scale left-right model, which naturally embeds this B-L symmetry. In particular, we make a detailed study of the lepton collider implications of the neutral (H3) and doubly-charged (H±±) scalars from the right-handed triplet Higgs that is responsible for the spontaneous breaking of the B-L symmetry and implementing the seesaw mechanism. Due to mixing with other scalars, the neutral scalar H3 could acquire sizable flavor violating couplings to the charged leptons. Produced on-shell or off-shell at the planned e+e- colliders, it would induce distinct lepton flavor violating signals like e+e-→μ±τ(+H3), with the couplings probed up to ∼10-4 for a wide range of neutral scalar mass, which is well beyond the reach of current searches for charged lepton flavor violation. The Yukawa couplings of the doubly-charged scalar H±± to the charged leptons might also be flavor violating, which is correlated to the heavy right-handed neutrino masses and mixings. With a combination of the pair, single and off-shell production of H±± like e+e-→H++H - , H±±eμ, μ±τ, the Yukawa couplings can be probed up to 10-3 at future lepton colliders, which is allowed by current lepton flavor data in a large region of parameter space. For both the neutral and doubly-charged cases, the scalar masses could be probed up to the few-TeV range in the off-shell channel.