We present a detailed study of the electric dipole moment of the neutron induced by a vacuum theta angle within the framework of QCD sum rules. At next-to-next-to-leading order in the operator product expansion, we find the result dn(θ)= 1.2 × 10-16θ̄e · cm, to approximately 40% precision. With the current experimental bound this translates into a limit on the theta parameter of θ̄ < 6 × 10-10. We compare this result with the long-standing estimates obtained within chiral perturbation theory, and observe a numerical similarity, but also significant differences in the source of the dominant contribution.
Bibliographical noteFunding Information:
We would like to thank I. Khriplovich, W. Marciano, M. Shifman, N. Uraltsev, and especially A. Vainshtein for many valuable discussions and comments. This work was supported in part by the Department of Energy under Grant No. DE-FG02-94ER40823.
- Electric dipole moments of nucleons
- QCD sum rules