Instanton-induced contributions of fractional twist to the cross section of hard gluon-gluon scattering in QCD

We study the instanton-induced cross section of hard gluon scattering in deep-inelastic kinematics. We find that the structure functions may possess numerically large nonperturbative contributions, which are related to Ringwald-type processes with the violation of chirality, and correspond to the exponential correction to the coefficient function in front of the parton distribution of the leading twist. Instanton-induced contributions are well defined for the structure function at the fixed value of the Bjorken scaling variable, and are probably absent in the moments. At intermediate virtualities of the order of $Q^2\sim {(30-50\mathrm{} \mathrm{GeV})}^2$ these essentially nonperturbative contributions of fractional twist reach large values, of order ${10}^0$-${10}^{-2\mathrm{}}$ of the perturbative cross section, and remain at the same time under theoretical control.