Abstract
Many new physics scenarios beyond 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. We show that such scalars could be effectively produced at future lepton colliders, either on shell or off shell depending on their mass, and induce lepton flavor violating (LFV) signals, i.e., e^{+}e^{-}→ℓ_{α}^{±}ℓ_{β}^{∓}(+H) with α≠β. 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. In particular, a scalar-loop induced explanation of the long-standing muon g-2 anomaly can be directly tested in the on-shell mode.
Highlights
Introduction.—The observation of neutrino oscillations [1] suggests that the lepton family numbers are violated
In the minimal extension of the standard model (SM) with Dirac neutrinos, charged lepton flavor violation (cLFV) rates are highly suppressed due to small neutrino masses. This makes the experimental searches for cLFV all the more interesting, because any observable effect must come from physics beyond the minimally extended SM related to the origin of neutrino mass
In this Letter, we show that such scenarios of neutral scalar-induced cLFV can be effectively probed in a model
Summary
Constraints, such as lα → lβγ, lα → 3lβ, 2lβlγ [1], only a few of them are directly relevant to the LFV prospects discussed below. On-shell LFV.—If kinematically allowed, the neutral scalar H can be directly produced at lepton colliders, in association with a pair of flavor-changing leptons through the couplings in Eq (1), i.e., eþe− → lÆα l∓β H (with α ≠ β), as shown in Fig. 1 (top panel). The MACS experiment [25] could exclude a large parameter space, as shown in the left panel of Fig. 3. As a result of the precise measurement of ae [26], the constraint on heμ is comparable to that from muonium oscillation, as shown in the left panel of Fig. 3.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
