Lepton Flavor Violation Induced by Neutral Scalar at Future Lepton Colliders

Many new physics scenarios beyond the Standard Model often necessitate the existence of a (light) neutral scalar H, which might couple to the charged leptons in a flavor violating way, while evading all existing constraints. Such scalars could be effectively produced at future lepton colliders like CEPC, ILC, FCC-ee and CLIC, either on-shell or off-shell, and induce lepton flavor violating (LFV) signals. We find that a large parameter space of the scalar mass and the LFV couplings can be probed, well beyond the current low-energy constraints in the lepton sector. The neutral scalar explanation of the muon g-2 anomaly could also be directly tested at future lepton colliders.