Resonance estimates of O(p6) low-energy constants and QCD short-distance constraints

Starting from the study of the low-energy and high-energy behaviors of the QCD three-point functions , and , several O(p(6)) low-energy constants of the chiral Lagrangian are evaluated within the framework of the lowest meson dominance (LMD) approximation to the large-NC limit of QCD. In certain cases, values that differ substantially from estimates based on a resonance Lagrangian are obtained. It is pointed out that the differences arise through the fact that QCD short-distance constraints are in general not correctly taken into account in the approaches using resonance Lagrangians. We discuss the implications of our results for the O(p(6)) counterterm contributions to the vector form factor of the pion and to the decay pi --> ev(e)gamma, and for the pion-photon-photon transition form factor.