π-η mixing from QCD sum rules

The q2 dependence of the π-η mixing amplitude is examined with the use of QCD sum rules. The linear slope of the mixing function θ(q2) is found to be much smaller than that for ϱ-ω mixing. Thus the mixing amplitude is approximately the same in the space-like region as in the time-like one, and one may neglect the q2 dependence of the mixing. A comparison between a hadron-meson, an effective chiral model, and the QCD sum rules approaches is made.