Weakly-induced strong CP-violation
  Weak interaction contributions to the strong theta parameter are revisited in the frame of a large-Nc Chiral Perturbation Theory. Focusing on the hadronic (eta,etaprime) \to pi pi amplitudes, we express these second-order corrections in terms of the CP-violating parameter in K \to pi pi decays to obtain Delta_w(theta) approx 10^{-17} at O(GF^2 epsilonprime). 
J. M. Gerard and P. Mertens
hep-ph hep-ex