Role of Nonperturbative Effects in Deep Inelastic Scattering Revisited
  Restrictions imposed on the (electromagnetic or weak) current operator by its commutation relations with the representation operators of the Poincare group are considered in detail. We argue that the present theory of deep inelastic scattering based on perturbative QCD does not take into account the dependence of the current operator on the nonperturbative part of the quark-gluon interaction which cannot be neglected even in leading order in $1/Q$, where $Q$ is the magnitude of the momentum transfer. 
Felix M. Lev