Charm CP Violation and the Electric Dipole Moments from the Charm Scale

TL;DR

This paper explores the implications of CP violation observed in charm decays for electric dipole moments, suggesting potential new physics effects and providing a theoretical framework for their analysis.

Contribution

It introduces a Ward-identity-based derivation of scalar pion-nucleon coupling induced by CP-odd interactions at the charm scale, linking charm CP violation to neutron EDM constraints.

Findings

CP asymmetry in D decays implies a neutron EDM 30-100 times larger than SM predictions.

Charm-induced neutron EDM is estimated around 10^{-31} e*cm in the SM.

Interference effects at the charm scale can generate observable EDM signals.

Abstract

The reported CP asymmetry in D->K^+K^- / pi^+pi^- is argued to be too large to naturally fit the SM. If so, a new source of CP violation is implied in the Delta C=1 sector with a milliweak strength. CP-odd interactions in the flavor-diagonal sector are strongly constrained by the EDMs placing severe limitations on the underlying theory. While the largest effects usually come from the New Physics energy scale, they are strongly model-dependent. Yet the interference of the CP-odd forces manifested in D decays with the conventional CP-even Delta C=1 weak interaction generates at the charm scale a background level. It has been argued that the d_n in the SM is largely generated via such an interference, with mild KM-specific additional suppression. The reported CP asymmetry is expected to generate d_n of 30 to 100 times larger than in the SM, or even higher in certain model yet not quite natural examples. In the SM the charm-induced loop-less |d_n| is expected around 10^{-31}e*cm. On the technical side, we present a compact Ward-identity--based derivation of the induced scalar pion-nucleon coupling in the presence of the CP-odd interactions, which appears once the latter include the right-handed light quarks.