All current experiments searching for an electron electric dipole moment (EDM) $d_e$ are performed with atoms and diatomic molecules. Motivated by significant recent progress in searches for an EDM-type signal in diatomic molecules with an uncompensated electron spin, we provide an estimate for the expected signal in the Standard Model due to the Cabibbo-Kobayashi-Maskawa (CKM) phase. We find that the main contribution originates from the effective electron-nucleon operator $\overline{e}i{\gamma }_{5}e\overline{N}N$, induced by a combination of weak and electromagnetic interactions at $O(G_F^2{\alpha }^2)$, and not by the CKM-induced electron EDM itself. When the resulting atomic $P,T$-odd mixing is interpreted as an equivalent electron EDM, this estimate leads to the benchmark $d_e^{\text{equiv}}(\text{CKM})\sim {10}^{-38}e\mathrm{cm}$.

• Received 11 December 2013

DOI:https://doi.org/10.1103/PhysRevD.89.056006