Cosmic rays interfacing astrophysics and particle physics

The development of Extensive Air Showers (EAS) is driven by the hadronic in teractions of the primary and secondary particles with the atmospheric nucl ei. Hence a careful analysis of the EAS appearance, in particular of the ha dronic component, provides valuable information on features of the hadronic interaction. Especially, in ultrahigh energy regions extending the energy limits of man-made accelerators and the experimental knowledge from collide r experiments, the hadronic interaction is subject of uncertainties and deb ates. Since the EAS development is dominantly governed by soft processes, w hich are not accessible to a perturbative QCD treatment, one has to rely on QCD inspired phenomenological interaction models, in particular on string models based on the Gribov-Regge theory, like VENUS, QGSJET and SIBYLL. Rec ent results of EAS experiments are scrutinised in terms of such models, use d as generators in the Monte Carlo EAS simulation code CORSIKA.