We show that combining the published Pierre Auger Observatory measurements of
the longitudinal_and_ lateral properties of UHE atmospheric showers, points to
an unforeseen change in the nature of particle interactions at ultrahigh
energy. A "toy model" of UHE proton-air interactions is presented which
provides the first fully consistent description of air shower observations. It
demonstrates that the observed energy dependence of the depth-of-shower-maximum
distribution may not indicate a transition to a heavier composition, as
commonly assumed. While fundamentally phenomenological, the model is based on
considerations of how the normal vacuum of QCD might be vaporized and chiral
symmetry restored by the extreme energy densities produced in UHE collisions.
Whatever its origin, understanding this unexpected phenomenon opens exciting
directions in particle physics and may impact Early Universe cosmology.Comment: Based on talk given Feb. 14, 2012 at UHECR 2012 - International
Symposium on Future Directions in UHECR Physics, CERN, Genev
