Space-Time Foam and Cosmic-Ray Interactions

Abstract

It has been proposed that propagation of cosmic rays at extreme-energy may be sensitive to Lorentz-violating metric fluctuations (``foam''). We investigate the changes in interaction thresholds for cosmic-rays and gamma-rays interacting on the CMB and IR backgrounds, for a class of stochastic models of spacetime foam. The strength of the foam is characterized by the factor (E/M_P)^a, where ``a'' is a phenomenological suppression parameter. We find that there exists a critical value of ``a'' (dependent on the particular reaction), below which the threshold energy can only be lowered, and above which the threshold energy may be raised, but at most by a factor of two. Thus, it does not appear possible in this class of models to extend cosmic-ray spectra significantly beyond their classical absorption energies. However, the lower thresholds resulting from foam may have signatures in the cosmic-ray spectrum. We also find that cosmic-ray energies cannot exceed the fundamental Planck scale, and so set a lower bound of 10^8 TeV on the context of this model for the scale of gravity. Finally, we comment in the apparent non-conservation of particle energy-momentum, and speculate on its re-emergence as dark energy in the foamy vacuum.

27 pages, 13 figures. Author added (Buniy), appendix added, and new section added, corrections made. To appear in Astroparticle Physics

References in corpus (3)

• Threshold effects and Planck scale Lorentz violation: combined constraints from high energy astrophysics
• Loop Quantum Gravity and Ultra High Energy Cosmic Rays
• Constraints on Lorentz Invariance Violating Quantum Gravity and Large Extra Dimensions Models using High Energy Gamma Ray Observations

Cited by in corpus (9)

• Modern tests of Lorentz invariance
• Quantum Spacetime Phenomenology
• Cosmic Rays from the Knee to the Highest Energies
• Ultra-High-Energy Cosmic Rays
• Bounds on length scales of classical spacetime foam models
• Constraints from cosmic rays on non-systematic Lorentz violation
• Propagation of cosmic rays in the foam-like Universe
• New test of Lorentz symmetry using ultrahigh-energy cosmic rays
• Quantum Decoherence of Photons in the Presence of Hidden U(1)s