Inclusive and diffractive structure functions at small x

In the semiclassical approach, inclusive and diffractive quark and gluon distributions are expressed in terms of correlation functions of Wilson loops. Each Wilson loop integrates the colour field strength in the area between the trajectories of two fast partons penetrating the proton. We introduce a specific model for averaging over the relevant colour held configurations. Within this model, all parton distributions at some low scale Q(0)(2) are given in terms of three parameters. Inclusive and diffractive structure functions at higher values of Q(2) are determined in a leading-order QCD analysis. In both cases, the evolution is driven by a large gluon distribution. A satisfactory description of the structure functions F-2(x, Q(2)) and F-2(D(3)) (xi, beta, Q(2)) is obtained. The observed rise of F-2(D(3)) with xi is parametrized by a non-perturbative logarithmic energy dependence, compatible with unitarity. In our analysis, the observed rise of F-2 at small, x is largely due to the same effect. (C) 1999 Elsevier Science B.V.