Instantons in deep-inelastic scattering: The simplest process

Instanton calculations in QCD are generically plagued by infrared divergencies associated with the integration over the instanton size ϱ. Here, we demonstrate explicitly that the typical inverse hard momentum scale Q^-1 in deep-inelastic scattering provides a dynamical infrared cutoff for the size parameter ϱ. Hence, deep-inelastic scattering may be viewed as a distinguished process for studying manifestations of QCD instantons. For clarity, we restrict the explicit discussion to the simplest chirality-violating process, y ^* + g → overlineq_L + q_R. We calculate the corresponding fixed-angle cross section as well as the contributions to the gluon structure functions, F_2g and F_Lg , within standard instanton perturbation theory in leading semi-classical approximation. To this approximation, fixed-angle scattering processes at high Q² are reliably calculable. In the Bjorken limit, the considered instanton-induced process gives a scaling contribution to F_2g( x, Q²⁾ and the Callan-Gross relation holds.