Charged lepton flavor violation in light of muon $$g-2$$

Abstract

AbstractThe recent confirmation of the muon $$g-2$$ g - 2 anomaly by the Fermilab $$g-2$$ g - 2 experiment may harbinger a new era in $$\mu $$ μ and $$\tau $$ τ physics. In the context of general two Higgs doublet model, the discrepancy can be explained via one-loop exchange of sub-TeV exotic scalar and pseudoscalars, namely H and A, that have flavor changing neutral couplings $$\rho _{\tau \mu }$$ ρ τ μ and $$\rho _{\mu \tau }$$ ρ μ τ at $$\sim 20$$ ∼ 20 times the usual tau Yukawa coupling, $$\lambda _\tau $$ λ τ . Taking $$\rho _{\ell \ell ^\prime }\sim \lambda _{ \mathrm min(\ell , \ell ^\prime )}$$ ρ ℓ ℓ ′ ∼ λ m i n ( ℓ , ℓ ′ ) , we show that the above solution to muon $$g-2$$ g - 2 then predicts enhanced rates of various charged lepton flavor violating processes, which should be accessible at upcoming experiments. We cover muon related processes such as $$\mu \rightarrow e \gamma $$ μ → e γ , $$\mu \rightarrow eee$$ μ → e e e and $$\mu N \rightarrow e N$$ μ N → e N , and $$\tau $$ τ decays $$\tau \rightarrow \mu \gamma $$ τ → μ γ and $$\tau \rightarrow \mu \mu \mu $$ τ → μ μ μ . A similar one-loop diagram with $$\rho _{e\tau }= \rho _{\tau e} = \mathcal{O}(\lambda _e)$$ ρ e τ = ρ τ e = O ( λ e ) induces $$\mu \rightarrow e\gamma $$ μ → e γ , bringing the rate right into the sensitivity of the MEG II experiment. The $$\mu e\gamma $$ μ e γ dipole can be probed further by $$\mu \rightarrow 3e$$ μ → 3 e and $$\mu N \rightarrow eN$$ μ N → e N . With its promised sensitivity range and ability to use different nuclei, the $$\mu N \rightarrow eN$$ μ N → e N conversion experiments can not only make discovery, but access the extra diagonal quark Yukawa couplings $$\rho _{qq}$$ ρ qq . For the $$\tau $$ τ lepton, we find that $$\tau \rightarrow \mu \gamma $$ τ → μ γ would probe $$\rho _{\tau \tau }$$ ρ τ τ down to $$\lambda _\tau $$ λ τ or lower, while $$\tau \rightarrow 3\mu $$ τ → 3 μ would probe $$\rho _{\mu \mu }$$ ρ μ μ to $$\mathcal{O}(\lambda _{\mu })$$ O ( λ μ ) .