Leptonic dipole operator with $Γ_2$ modular invariance in light of Muon $(g-2)_μ$

Abstract

We have studied the leptonic EDM and the LFV decays relating with the recent data of anomalous magnetic moment of muon, $(g-2)_μ$ in the leptonic dipole operator. We have adopted the successful $Γ_2$ modular invariant model by Meloni-Parriciatu as the flavor symmetry of leptons. Suppose the anomaly of $(g-2)_μ$, $Δa_μ$ to be evidence of New Physics (NP), we have related it with the anomalous magnetic moment of the electron $Δa_e$, the electron EDM $d_e$ and the $μ\to e γ$ decay. We found that the NP contributions to $Δa_{e(μ)}$ are proportional to the lepton masses squared likewise the naive scaling $Δa_\ell \propto m^2_\ell$. The experimental constraint of $|d_e|$ is much tight compared with the one from the branching ratio $\mathcal{B} (μ\to e γ)$ in our framework. Supposing the phase of our model parameter $δ_α$ for the electron to be of order one, we have estimated the upper-bound of $\mathcal{B}(μ\to e γ)$, which is at most $10^{-21}-10^{-20}$. If some model parameters are real, leptonic EDMs vanish since the CP phase of the modular form due to modulus $τ$ does not contribute to the EDM. However, we can obtain $\mathcal{B} (μ\to e γ)\simeq 10^{-13}$ with non-vanishing $d_e$ in a specific case. The imaginary part of a parameter can lead to $d_e$ in the next-to-leading contribution. The predicted electron EDM is below $10^{-32}$e\,cm, while $\mathcal{B} (μ\to e γ)$ is close to the experimental upper-bound. The branching ratios of $τ\to eγ$ and $τ\to μγ$ are also discussed.