Soft and hard Pomeron in the structure function of the proton at low x and low Q(2)

We study inclusive electroproduction on the proton at low x and low Q(2) using a soft and a hard Pomeron. The contribution of the soft Pomeron is based on the Stochastic Vacuum Model; in which a nonperturbative dipole-dipole cross section can be calculated by means of a gauge invariant gluon field strength correlator. To model the hard Pomeron exchange we phenomenologically extend the leading order evolution of a power-behaved structure function, F2 proportional to x^(-lambda), proposed by Lopez and Yndurain. This extension allows to consider both the case Q(2) = 0 and the region of higher Q(2) on the basis of the same parametrization. A good simultaneous fit to the data on F2 and on the cross section sigma(gamma p) of real photoproduction is obtained for lambda = 0.37. With four parameters we achieve a chi(2)/d.o.f. = 0.98 for 222 data points. In addition, we use our model of the inclusive gamma*p interaction to compute the longitudinal structure function F(L).