The photon-photon interaction at low $x$ in the theory of reggeized gluons with a running coupling and $N_{c}\to\infty$

Abstract

The forward elastic amplitude for scattering of real and weakly virtual photons is studied in the framework of the theory of reggeized gluons, with large $N_{c}$ and a running coupling constant introduced in the manner which preserves the bootstrap condition. Transition from a single to multiple pomeron exchanges is observed as $x$ gets smaller. For very low $x$ the amplitude aquires an eikonal form. The photon structure function reveals a strong violation of scaling: it grows as $Q^{2}$. As a function of $x$ it behaves as $(\ln(1/x)\ln\ln(1/x))^{2}$. Correspondingly the cross-section for physical photons grows with energy as $(\ln s\ln\ln s)^{2}$. Hadronic structure functions and cross-sections are also briefly discussed.