  Large scale airshower simulations around the GZK cutoff are performed. An
extensive analysis of the behaviour of the various subcomponents of the cascade
is presented. We focus our investigation both on the study of total and partial
multiplicities along the entire atmosphere and on the geometrical structure of
the various cascades, in particular on the lateral distributions. The
possibility of detecting new physics in Ultra High Energy Cosmic Rays (UHECR)
at AUGER is also investigated. We try to disentangle effects due to standard
statistical fluctuations in the first proton impact in the shower formation
from the underlying interaction and comment on these points. We argue that
theoretical models predicting large missing energy may have a chance to be
identified, once the calibration errors in the energy measurements are resolved
by the experimental collaborations, in measurements of inclusive
multiplicities.
