Loop-Less Electric Dipole Moment of the Nucleon in the Standard Model

TL;DR

This paper reveals a previously overlooked tree-level contribution to the neutron's electric dipole moment within the Standard Model, arising from bound-state effects and independent of short-distance loops, with implications for CP-violation studies.

Contribution

It identifies a novel, tree-level, bound-state effect generating the neutron EDM in the Standard Model, independent of quark mass splitting and short-distance penguin loops.

Findings

Estimated neutron EDM around 10^(-31) e*cm

Contribution exists at tree level without penguin loops

Implications for CP-violation in D decays

Abstract

We point out that the electric dipole moment of the neutron in the Standard Model is generated already at tree level to the second order in the weak interactions due to bound-state effects, without short-distance Penguin loops. The related contribution has a regular nonvanishing chiral limit and does not depend on the mass splitting between s and d quarks. We estimate it to be roughly 10^(-31)e*cm and expect a more accurate evaluation in the future. We comment on the connection between d_n and the direct CP-violation in D decays.