Loop Quantum Gravity Effects on the High Energy Cosmic Ray Spectrum
  Recent observations on ultra high energy cosmic rays (those cosmic rays with energies greater than $\sim 4 \times 10^{18}$ eV) suggest an abundant flux of incoming particles with energies above $1 \times 10^{20}$ eV. These observations violate the Greisen-Zatsepin-Kuzmin cutoff. To explain this anomaly we argue that quantum-gravitational effects may be playing a decisive role in the propagation of ultra high energy cosmic rays. We consider the loop quantum gravity approach and provide useful techniques to establish and analyze constraints on the loop quantum gravity parameters arising from observational data. In particular, we study the effects on the predicted spectrum for ultra high energy cosmic rays and conclude that is possible to reconcile observations. 
Jorge Alfaro (Facultad de F\'isica, Pontificia Universidad Cat\'olica   de Chile), Gonzalo A. Palma (Department of Applied M...