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VOLUME 92 | ISSUE 10 | PAGE 777

-195.2008.2
Photon-pion transition form factor at high photon virtualities within the nonlocal chiral quark model
Abstract
Recently, the BABAR collaboration reported the measurments of the photon-pion transition form factor F_{\pi\gamma\gamma^{\ast}}\left(Q^{2}\right) , which are in strong contradiction to the predictions of the standard factorization approach to perturbative QCD. In the present work, based on a nonperturbative approach to the QCD vacuum and on rather universal assumptions, we show that there exists two asymptotic regimes for the pion transition form factor. One regime with asymptotics F_{\pi\gamma^{\ast}\gamma}\left(Q^{2}\right) \sim1/Q^{2} corresponds to the result of the standard QCD factorization approach, while other violates the standard factorization and leads to asymptotic behavior as F_{\pi\gamma^{\ast}\gamma}\left(Q^{2}\right) \sim\ln\left(Q^{2}\right)
/Q^{2}. Furthermore, considering specific nonlocal chiral quark models, we find the region of parameters, where the existing CELLO, CLEO and BABAR data for the pion transition form factor are successfully described.