Theory of gauge-invariant operators: Their renormalization andS-matrix elements

Abstract
The renormalization of gauge-invariant operators in Yang-Mills theories is discussed. An important property of the relevant Ward identities is used to show that the coupling of a subset of these (those which do not vanish by the equations of motion) to other operators takes a simple form. It is also shown that the renormalization constants appropriate to this set are independent of the gauge parameter. It is demonstrated that in certain important applications, for example the calculation of deep-inelastic scattering using the operator-product expansion, only the operators in this set are physically relevant.