Probing the QCD pomeron in high-energy $\gamma^*\gamma^*$ collisions

Abstract

Based on the color dipole representation, we investigate consequences for the $\gamma^{*}\gamma^{*},\gamma^{*}\gamma$ scattering of the finding by Fadin, Kuraev and Lipatov that incorporation of asymptotic freedom into the BFKL equation makes the QCD pomeron a series of isolated poles in the angular momentum plane. We present parameter-free predictions for the vacuum exchange contribution to the photon structure function which agree well with OPAL and L3 determinations. A good agreement is found between our predictions for the energy and photon virtuality dependence of the photon-photon cross section $\sigma^{\gamma^*\gamma^*}(W,Q^2,P^2)$ and the recent data taken by the L3 Collaboration.