The operator-product expansion away from euclidean region

Abstract

The role of the operator-product expansion in QCD calculations is discussed. Approximating the two-point correlation function by several terms and assuming an upper bound on the truncation error along the euclidean ray, we consider two model situations to examine how the bound develops with increasing deflection from the euclidean ray towards the cut. We obtain explicit bounds on the truncation error and show how they worsen with the increasing deflection. The result does not support the believe that the remainder is constant for all angles in the complex energy plane. Further refinements of the formalism are dicussed.