Standard Model prediction for paramagnetic EDMs

Abstract

Standard Model $CP$ violation associated with the phase of the Cabibbo-Kobayashi-Maskawa quark mixing matrix is known to give small answers for the EDM observables. Moreover, predictions for the EDMs of neutrons and diamagnetic atoms suffer from considerable uncertainties. We point out that the $CP$-violating observables associated with the electron spin (paramagnetic EDMs) are dominated by the combination of the electroweak penguin diagrams and $\Delta I=1/2$ weak transitions in the baryon sector, and are calculable within chiral perturbation theory. The predicted size of the semileptonic operator $C_S$ is $7\times 10^{-16}$ which corresponds to the equivalent electron EDM $d_e^{\mathrm{eq}}=1.0\times 10^{-35}e\mathrm{cm}$. While still far from the current observational limits, this result is three orders of magnitude larger than previously believed.

Comments: 4 pages, 2 figures. v2: an overall sign error fixed and references added