EXCLUSIVE PROCESSES AT INTERMEDIATE-ENERGY, QUARK-HADRON DUALITY AND THE TRANSITION TO PERTURBATIVE QCD

Experiments at CEBAF will scan the intermediate-energy region of the Q CD dynamics for the nucleon form factors and for Compton Scattering. T hese experiments will definitely clarify the role of resummed perturba tion theory and of quark-hadron duality (QCD sum rules) in this regime . With this perspective in mind, we review the factorization theorem o f perturbative QCD for exclusive processes at intermediate energy scal es, which embodies the transverse degrees of freedom of a parton and t he Sudakov resummation of the corresponding large logarithms. We conce ntrate on the pion and proton electromagnetic form factors and on pion Compton scattering. New ingredients, such as the evolution of the pio n wave function and the complete two-loop expression of the Sudakov fa ctor, are included. The sensitivity of our predictions to the infrared cutoff for the Sudakov evolution is discussed. We also elaborate on Q CD sum rule methods for Compton Scattering, which provide an alternati ve description of this process. We show that, by comparing the local d uality analysis to resummed perturbation theory, it is possible to des cribe the transition of exclusive processes to perturbative QCD.