Large distance behaviour of light cone operator product in perturbative and nonperturbative QCD regimes

Abstract

We evaluate the coordinate space dependence of the matrix elements of the commutator of the electromagnetic and gluon currents in the vicinity of the light-cone but at large distances within the parton model, DGLAP, the resummation approaches to the small x behaviour of DIS processes, and for the Unitarity Bound. We find that an increase of the commutator with relative distance $py$ as $\propto (py)f(py,y^2=t^2-r^2)$ is the generic property of QCD at small but fixed space-time interval $y^2=t^2-r^2$ in perturbative and nonperturbative QCD regimes. We explain that the factor $py$ follows within the dipole model (QCD factorization theorem) from the properties of Lorents transformation. The increase of $f(r)$ disappeares at central impact parameters if cross section of DIS may achieve the Unitarity Limit. We argue that such long range forces are hardly consistent with thermodynamic equilibrium while a Unitarity Limit may signal equilibration. Possible implications of this new long range interaction are briefly discussed.