Dynamics of PP collisions at small impact parameters, universality of cross sections of hadron-hadron collisions and critical phenomena at superhigh energies

Studies of the small x dynamics at HERA energies allow to quantify the range of momentum transfers and energies for which the strength of the interaction approaches the maximum strength allowed by unitarity in the gluon channel (black disk limit - BDL). Implications for the proton-proton interactions at collider energies (Tevatron, LHC) include a dominance of BDL up to transverse momenta of hadrons (jets) in the final state ∼ few GeV for collision at small impact parameters, and explanation of the proximity of the impact factor of pp interaction to one at small impact parameters, leading to universality of cross sections at superhigh energies. We discuss briefly the theoretical challenges in the applications of pQCD to small x phenomena, the similarity between small x physics and critical phenomena, and new QCD phenomena related to this puzzle.