Twist-4 effects in electroproduction: Canonical operators and coefficient functions

The interpretation of observed scaling violations in leptoproduction is complicated by the possible presence of significant higher-twist effects. We refine the machinery of the operator-product expansion sufficiently for a study of twist-4 effects. In particular, we introduce and review the advantages of a special, "canonical" basis. We demonstrate that the canonical basis is adequate for the necessary twist-4 perturbative calculations, and calculate the operators' tree-level coefficient functions in electroproduction. Our results establish a framework within which careful analysis of more accurate data can provide information regarding correlations among the constituents of the proton.