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MathematicalPhysicist

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What has changed since then? have we found a different theoretical approach to explain exclusive phenomena?In particular the PQCD results for the pion form factor, the transition form factor ##F_{\gamma \pi}(Q^2)##, and the ##\gamma\gamma \to \pi \pi## amplitudes are theorems of QCD and are as rigorous as the predictions for ##R_{e^+e^-}(s)##, the evolution equations for structure functions, etc. Although the perturbative QCD analysis is complex, it's hard to imagine that any other viable description would be simpler. At this point there is no other theoretical approach which provides as comprehensive a description of exclusive phenomena.