Power Corrections and Higher Twists in QCD

People believe QCD to be the theory of strong interactions for a variety of reasons. Firstly, SU(3) of color is a subgroup of SU(5); second, it has instantons and a variety of other interesting topological properties; and, lastly, it agrees with high energy experiments. But on this last point, one must confess that there are a variety of obstacles that have thus far precluded any overwhelmingly convincing numerical confrontation with data. Theorists divide the sources of troubles into several classes. One of these is the power or higher twist corrections. I describe here a tentative approach of a systematic analysis of power corrections. The analysis is motivated by, and generalizes on, the operator product analysis of leptoproduction. In essence, I try to identify the appropriate set of process-independent, non-perturbative functions that characterize long-distance physics; these are to be convoluted with calculable short-distance amplitudes via an algorithm that generalizes the long distance-short distance factorization for the scaling limit.