Vector meson dominance and deep inelastic scattering at low and medium Q squared

Abstract

We argued that deep inelastic scattering (DIS) at small values of Q squared is an essentially nonperturbative process and can be described, partially at least, by the vector meson dominance (VMD) model. We showed by the straightforward calculation that VMD model alone can successfully explain data on structure functions of DIS in a broad interval of x (5e-2 - 1e-4) for the region Q squared < 1 GeV squared. For a description of data at larger Q squared we used the two-component (VMD + perturbative QCD) approach. We showed that these two components can be separated if VMD is used in the aligned jet version. We took into account, in calculations of VMD component of structure functions, the excited states of the rho-meson and nondiagonal transitions between different members of the rho-meson family. Amplitudes of these transitions were obtained using a formalism of the light-front Bethe-Salpeter equation and the method of diffraction-scattering eigenstates. The perturbative QCD component was calculated using a framework of the colour dipole model with the dipole cross section having a Regge-type energy dependence. We presented results of the detailed comparison of our predictions with experimental data for structure functions of the nucleon. We obtained also approximate predictions for the structure functions in the region of very small x, up to 1e-9, and showed that nonperturbative component at such values of x is still relatively large and must be taken into account if Q squared is about few GeV squared or less.