Cross Section Fluctuations of Photon Projectile in Generalized Vector Meson Dominance Model

Abstract

We explain that the generalized vector meson dominance (GVMD) model is successful in describing hard high energy processes because it contains expected in QCD Color Coherent Phenomena. Within the model, which reproduces Bjorken scaling and nuclear shadowing for deep inelastic processes, we calculate $P_γ(σ,Q^2)$, the probability for the photon to interact with a target with the cross section $σ$. We find that within the GVMD model the virtual photon has two main components: the ''hard'' one with the 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 $P_γ(σ,Q^2)$ similar to that within the parton model and suggests the conspiracy between hard and soft QCD at $Q^2 > 1$ GeV$^2$. We study the limit $σ\to 0$ and show, that $P_γ(σ,Q^2) \propto 1/ σ$ in both 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.