Cross section fluctuations of a photon projectile in the generalized vector meson dominance model

Abstract

We explain that the generalized vector meson dominance (GVMD) models successful in the theoretical description of photoproduction and electroproduction in high energy processes effectively implement color coherent phenomena expected in QCD. Within a model, which reproduces Bjorken scaling and nuclear shadowing for deep inelastic processes, we calculate ${P}_{\ensuremath{\gamma}}(\ensuremath{\sigma}{,Q}^{2}),$ the probability for a photon to interact with a target with the cross section \ensuremath{\sigma}. We find that within the GVMD model the virtual photon has two main components: the ``hard'' one with a small cross section of the order of ${1/Q}^{2}$ and the high probability and the ``soft'' one with a typical hadronic cross section with the probability suppressed by the factor of ${1/Q}^{2}.$ Thus the GVDM model produces ${P}_{\ensuremath{\gamma}}(\ensuremath{\sigma}{,Q}^{2})$ similar to that within the parton model and suggests the interplay between hard and soft QCD at ${Q}^{2}>1{\mathrm{GeV}}^{2}.$ We study the limit $\stackrel{\ensuremath{\rightarrow}}{\ensuremath{\sigma}}0$ and show that ${P}_{\ensuremath{\gamma}}(\ensuremath{\sigma}{,Q}^{2})\ensuremath{\propto}1/\ensuremath{\sigma}$ in both the GVMD model and QCD. Thus similarly to the parton model the GVMD model predicts the color transparency phenomenon. This is an indirect indication that Bjorken scaling, color transparency and shadowing in nuclei in DIS are closely related.