Effect of binding in deep inelastic scattering revisited

In the present theories of deep inelastic lepton-nucleon scattering (DILNS) the Bjorken limit of DILNS can be described in the framework of perturbative QCD and the leading order of the perturbation theory is the parton model. However the current operator in the parton model does not properly commute with the representation operators corresponding to the Lorentz group, space reflection and time reversal, and therefore Lorentz invariance, P invariance and T invariance of the current operator are broken. To investigate the breaking of these symmetries we consider a model in which the current operator explicitly satisfies extended Poincare invariance, cluster separability and current conservation. It is shown that due to binding of quarks in the nucleon the Bjorken variable x no longer can be interpreted as the internal light cone momentum fraction \xi even in the Bjorken limit. As a result, the data on DILNS alone do not make it possible to determine the \xi distribution of quarks in the nucleon. It is also possible to give a natural qualitative explanation of the fact that in the parton model the values given by the sum rules exceed the corresponding experimental quantities while the quark contribution to the nucleon momentum and spin is underestimated