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Recent BaBaR data on the pion transition form factor, whose Q^2 dependence ismuch steeper then predicted by asymptotic Quantum Chromodynamics (QCD), havecaused a renewed interest in its theoretical description. We present here aformalism based on a model independent low energy description and a high energydescription based on QCD, which match at a scale Q_0. The high energydescription incorporates a flat pion distribution amplitude, phi(x)=1, at thematching scale Q_0 and QCD evolution from Q_0 to Q>Q_0. The flat piondistribution is connected, through soft pion theorems and chiral symmetry, tothe pion valance parton distribution at the same low scale Q_0. The procedureleads to a good description of the data, and incorporating additional twistthree effects, to an excellent description of the data.

The pion transition form factor and the pion distribution amplitude