Chiral anomaly, triangle loop and the γγ* →πo transition form factor

The recent BaBar measurements of the γ+γ* → πo form factor show spectacular deviation from perturbative QCD computations for large space-like Q2. At 34 GeV2 the data are more than 50% larger than theoretical predictions. Stimulated by these new experimental results, we revisit our previous paper on triangle loop effects related to chiral anomaly, and apply our method to the γ+γ* → πo transition form factor measured in the single tag mode e+ + e- → e+ + e- + πo with one highly virtual photon γ*. The resultant form factor F(Q2)- which depends on only one parameter (the mass m of up, down quark circulating in the triangle loop) behaves like (m2/Q2) x [ln(Q2/m2)]2- shows a striking agreement with BaBar data for m ∼ 132 MeV. The rising logarithm squared form factor, surprisingly unnoticed in the literature, is in sharp contrast with the rather flat ones derived from perturbative QCD approaches. (author)