  Ground based observations appear to indicate that Ultra High Energy Cosmic
Rays (UHECR) of the highest energies (>10^{18.7} eV) consist of heavy particles
-- shower depth and muon production data both pointing towards this conclusion.
On the other hand, cosmic-ray arrival directions at energies >10^{18.9} eV
exhibit a dipole anisotropy, which disfavors heavy composition, since higher-Z
nuclei are strongly deflected by the Galactic magnetic field, suppressing
anisotropy. This is the composition problem of UHECR. One solution could be the
existence of yet-unknown effects in proton interactions at center-of-mass (CM)
energies 50 TeV, which would alter the interaction cross section and the
multiplicity of interaction products, mimicking heavy primaries. We study the
impact of such changes on cosmic-ray observables using simulations of Extensive
Air-Shower (EAS), in order to place constrains on the phenomenology of any new
effects for high energy proton interactions that could be probed by \sqrt{s}>50
TeV collisions. We simulate showers of primaries with energies in the range
10^{17} - 10^{20} eV using the CORSIKA code, modified to implement a possible
increase in cross-section and multiplicity in hadronic collisions exceeding a
CM energy threshold of 50 TeV. We study the composition-sensitive shower
observables (shower depth, muons) as a function of cross-section, multiplicity,
and primary energy. We find that in order to match the Auger shower depth
measurements by means of new hadronic collision effects alone (if extragalactic
UHECR are all protons even at the highest energies), the cross-section of
proton-air interactions has to be 800 mb at 140 TeV CM energy, accompanied by
an increase of a factor of 2-3 in secondary particles. We also study the muon
production of the showers in the same scenario.
