Nonpointlike-parton model with asymptotic scaling and with scaling violation at moderateQ2values

Abstract

A nonpointlike-parton model is formulated on the basis of the assumption of energy-independent total cross sections of partons and the current-algebra sum rules. No specific strong-interaction Lagrangian density is introduced in this approach. This model predicts asymptotic scaling for the inelastic structure functions of nucleons on the one hand and scaling violation at moderate ${Q}^{2}$ values on the other hand. The predicted scaling-violation patterns at moderate ${Q}^{2}$ values are consistent with the observed scaling-violation patterns. A numerical fit of ${F}_{2}$ functions is performed in order to demonstrate that the predicted scaling-violation patterns of this model at moderate ${Q}^{2}$ values fit the data, and to see how the predicted asymptotic scaling behavior sets in at various $x$ values. Explicit analytic forms of ${F}_{2}$ functions are obtained from this numerical fit, and are compared in detail with the analytic forms of ${F}_{2}$ functions obtained from the numerical fit of the quantum-chromodynamics (QCD) parton model. This comparison shows that this nonpointlike-parton model fits the data better than the QCD parton model, especially at large and small $x$ values. Nachtman moments are computed from the ${F}_{2}$ functions of this model and are shown to agree with data well. It is also shown that the two-dimensional plot of the logarithm of a nonsinglet moment versus the logarithm of another such moment is not a good way to distinguish this nonpointlike-parton model from the QCD parton model.