Percolation effects in very-high-energy cosmic rays.

Cosmic ray data at high energies present a number of well-known puzzles. At very high energies (E approximately 10(20) eV) there are indications of a discrepancy between ground array experiments and fluorescence detectors. On the other hand, the dependence of the depth of the shower maximum Xmax with the primary energy shows a change in slope (E approximately 10(17) eV) which is usually explained assuming a composition change. Both effects could be accounted for in models predicting that above a certain energy showers would develop deeper in the atmosphere. In this Letter we argue that this can be done naturally by including percolation effects in the description of the shower development, which cause a change in the behavior of the inelasticity K above E approximately 10(17) eV.