Lepton Electric Dipole Moment and Strong CP Violation

TL;DR

This paper reevaluates the contribution of the strong CP angle to lepton EDMs, including previously missing effects, and finds these contributions are much smaller than experimental sensitivities but larger than CKM effects.

Contribution

The authors include the CP-violating three meson coupling in the calculation, providing a more complete estimate of the strong CP angle's effect on lepton EDMs.

Findings

Revised electron EDM contribution: (2.2-8.6)×10^{-28} arθ e-cm

Estimated muon EDM: (0.5-1.8)×10^{-25} arθ e-cm

EDM contributions are below current experimental sensitivities

Abstract

Contribution of the strong CP angle, $\bar\theta$, to the Wilson Coefficients of electron and muon electric dipole moment (EDM) operators are discussed. Previously, $\bar\theta$ contribution to the electron EDM operator was calculated by Choi and Hong. However, the effect of CP-violating three meson coupling was missing there. We include this missing contribution for the first time in the literature, and reevaluate the Wilson coefficients of the lepton EDM operator. We obtain $d_e = - (2.2-8.6) \times 10^{-28} \bar\theta$ e-cm which is 15 - 70 % of the result obtained in Choi and Hong. We also estimated the muon EDM as $d_\mu = - (0.5-1.8) \times 10^{-25} \bar\theta$ e-cm. Using $|\bar\theta| \lesssim 10^{-10}$ suggested by the neutron EDM measurements, we obtain $|d_e| \lesssim 8.6 \times 10^{-38}$ e-cm and $|d_\mu| \lesssim 1.8 \times 10^{-35}$ e-cm. The $\bar\theta$ contribution to the muon EDM is much below the sensitivities of the current and near future experiments. Our result shows that the $\bar\theta$ contribution to $d_{e,\mu}$ can be larger than the CKM contributions by many orders of magnitude.