Cosmic-ray knee and diffuse gamma, e+ and pbar fluxes from collisions of cosmic rays with dark matter

In models with extra dimensions the fundamental scale of gravity M_D could be of order TeV. In that case the interaction cross section between a cosmic proton of energy E and a dark matter particle \chi will grow fast with E for center of mass energies \sqrt{2m_\chi E} above M_D, and it could reach 1 mbarn at E\approx 10^9 GeV. We show that these gravity-mediated processes would break the proton and produce a diffuse flux of particles/antiparticles, while boosting \chi with a fraction of the initial proton energy. We find that the expected cross sections and dark matter densities are not enough to produce an observable asymmetry in the flux of the most energetic (extragalactic) cosmic rays. However, we propose that unsuppressed TeV interactions may be the origin of the knee observed in the spectrum of galactic cosmic rays. The knee would appear at the energy threshold for the interaction of dark matter particles with cosmic protons trapped in the galaxy by \muG magnetic fields, and it would imply a well defined flux of secondary antiparticles and TeV gamma rays.