SHAPE OF PION DISTRIBUTION AMPLITUDE AND TRANSVERSE MOMENTUM IN HARD EXCLUSIVE PROCESSES

Inclusion of transverse momentum effects into the description of the pion-photon transition form factor is discussed. At low k⊥, a consistent description may be obtained within the light-front formalism. On the other hand, the large-k⊥ limit is most conveniently treated within the Sudakov parameterization framework. The third way of introducing k⊥ is based on the "local duality" approach motivated by QCD sum rules. It is shown that, while the local duality gives a correct (coinciding with the axial anomaly based prediction) result for the real photon point, a straightforward extension of the formulas of the modified factorization approach into the small virtualities domain produces a divergent result. It is pointed out that such lessons should be taken into account while constructing transverse-momentum-dependent schemes for inclusive processes.