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We propose an effective lagrangian for the coupling of the neutral pion withgluons whose strength is determined by a low energy theorem. We calculate thecontribution of the gluonic components arising from this interaction to thepion transition form factor $\gamma^*\gamma^*\to\pi^0 $ using the instantonliquid model to describe the QCD vacuum. We find that this contribution islarge and might explain the anomalous behavior of the form factor at largevirtuality of one of the photons, a feature which was recently discovered bythe BaBar Collaboration.

Gluonic components of the pion and the transition form factor $\gamma^*\gamma^*\to\pi^0 $

Gluonic components of the pion and the transition form factor $\gamma^\gamma^\to\pi^0 $