We demonstrate that the QCD sum rule method can be successfully applied to the calculation of CP-odd electromagnetic observables induced by a vacuum θ-angle. We implement the approach in calculating the electric dipole moment of the rho meson to ∼ 30% precision, and find that the result can also be explicitly related to the vacuum topological susceptibility.
Bibliographical noteFunding Information:
We would like to thank M. Shifman and 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.