Do form factors at largeQ2and structure functions at largexnecessarily involve far-off-mass-shell quarks?

Abstract

We study the question of small or large virtuality of the partons involved in elastic form factors at large ${q}^{2}$ and in deep-inelastic lepton scattering at $x\ensuremath{\rightarrow}1$. We consider two classes of models, both allowed by kinematics: the soft ones, small-virtuality models (SVM), where all partons are near the mass shell, and the hard ones, high-virtuality models (HVM), where at least one active parton is far off the mass shell. Taking the Bethe-Salpeter wave function as input, we compare the kinematical and analytical properties of SVM and HVM in the above processes, using successively covariant formalism and old-fashioned perturbation theory at infinite momentum. Both models lead to the Drell-Yan-West relation, but Bloom-Gilman duality looks more natural in SVM. We apply our analysis to the recent quantum-chromodynamic approaches of asymptotic form factors.