Deep inelastic scattering and "elastic" diffraction

Abstract

We examine the total cross section of virtual photons on protons, ${\sigma }_{{\gamma }^{\ast }p}(W^2,Q^2)$, at low $x\cong Q^2/W^2\ll 1$ and its connection with ``elastic'' diffractive production ${\gamma }_{T,L}^{\ast }p\to X_{T,L}^{J=1}p$ in the two-gluon exchange dynamics for the virtual forward Compton scattering amplitude. Solely based on the generic structure of two-gluon exchange, we establish that the cross section is described by the (imaginary part of the) amplitude for forward scattering of $q\bar{q}$ vector states, $(q\bar{q}{)}_{T,L}^{J=1}p\to (q\bar{q}{)}_{T,L}^{J=1}p$. The generalized vector dominance/color dipole picture (GVD/CDP) is accordingly established to only rest on the two-gluon-exchange generic structure. This is explicitly seen by the sum rules that allow one to directly relate the total cross section to the cross section for elastic diffractive forward production, ${\gamma }_{T,L}^{\ast }p\to (q\bar{q}{)}_{T,L}^{J=1}p$, of vector states.

24 pages, latex file with three eps figures. BI-TP 2002/21