Strong CP violation in nuclear physics

TL;DR

This paper discusses the importance of short-distance operators in CP-violating nuclear forces, challenging the naive long-range dominance assumption, and explores implications for electric dipole moments and axion searches.

Contribution

It introduces the necessity of a leading-order short-distance operator in CP-violating nuclear forces, revising the traditional long-range dominance perspective.

Findings

Short-distance operators significantly affect electric dipole moments.

Renormalization arguments establish the need for a short-distance contribution.

Implications for axion search experiments are discussed.

Abstract

Electric dipole moments of nuclei, diamagnetic atoms, and certain molecules are induced by CP-violating nuclear forces. Naive dimensional analysis predicts these forces to be dominated by long-range one-pion-exchange processes, with short-range forces entering only at next-to-next-to-leading order in the chiral expansion. Based on renormalization arguments we argue that a consistent picture of CP-violating nuclear forces requires a leading-order short-distance operator contributing to ${}^1S_0$-${}^3P_0$ transitions, due to the attractive and singular nature of the strong tensor force in the ${}^3P_0$ channel. The short-distance operator leads to $\mathcal O(1)$ corrections to static and oscillating, relevant for axion searches, electric dipole moments. We discuss strategies how the finite part of the associated low-energy constant can be determined in the case of CP violation from the QCD theta term by the connection to charge-symmetry violation in nuclear systems.