Contemporary models of high energy interactions: present status and perspectives

Modern approaches to the description of high energy hadronic and nuclear, collisions are reviewed in connection with extensive air shower (EAS) physics. Special attention is devoted to the so-called semihard partonic processes which appear to dominate the interactions at very high. energies. It is shown that a corresponding treatment can be developed-in the framework of the Gribov-Regge approach, introducing a concept of 'semihard Pomeron', the latter being a t-channel iteration of the phenomenological 'soft' Pomeron and QCD parton ladder. A comparison is made with the QCD eikonal (mini-jet) scheme and essential differences as well as observable consequences for EAS development are analysed in detail. The role of nonlinear interaction contributions described by enhanced Pomeron diagrams is also investigated. It is demonstrated that such diagrams provide important screening corrections to the interaction mechanism and allow us to resolve a seeming contradiction between realistic parton momentum distributions and observed energy dependence of hadron-hadron cross sections. A modification of-the standard scheme by correct treatment of energy-momentum sharing mechanism in hadronic collisions is also considered. Finally, we discuss possible ways to discriminate between the alternative approaches.