Muon production and string percolation effects in cosmic rays at the   highest energies
  Ultra High Energy Cosmic Rays with energies above ~ 10^18 eV provide an unique window to study hadronic interactions at energies well above those achieved in the largest man-made accelerators. We argue that at those energies string percolation may occur and play an important role on the description of the induced Extensive Air Showers by enhancing strangeness and baryon production. This leads to a significant increase of the muon content of the cascade in agreement with recent data collected at UHECR experiments. In this work, the effects of string percolation in hadronic interactions are implemented in an EAS code and their impact on several shower observables is evaluated and discussed. 
J. Alvarez-Mu\~niz, L. Cazon, R. Concei\c{c}\~ao, J. Dias de Deus, C.   Pajares, M. Pimenta
hep-ph astro-ph.HE