Problems with Nonperturbative Effects in Deep Inelastic Scattering
  We consider restrictions imposed on the (electromagnetic or weak) current operator by its commutation relations with the representation operators of the Poincare group and show that the nonperturbative part of the current operator contributes to deep inelastic scattering even in leading order in $1/Q$ where $Q$ is the magnitude of the momentum transfer. Some consequences of this result are discussed. 
Felix M. Lev