Space–time foam and cosmic-ray interactions |
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| Authors: | Marcin Jankiewicz Roman V Buniy Thomas W Kephart Thomas J Weiler |
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| Institution: | Department of Physics and Astronomy, Vanderbilt University, Nashville, TN 37235, USA |
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| 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 space–time foam. The strength of the foam is characterized by the factor (E/MP)a, where a is a phenomenological suppression parameter. We find that there exists a critical value of a (dependent on the particular reaction: acrit 3 for cosmic-rays, 1 for gamma-rays), 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. In the context of this foam model, we find that cosmic-ray energies cannot exceed the fundamental Planck scale, and so set a lower bound of 108 TeV for the scale of gravity. We also find that suppression of p→pπ0 and γ→e?e+ “decays” favors values a acrit. Finally, we comment on the apparent non-conservation of particle energy–momentum, and speculate on its re-emergence as dark energy in the foamy vacuum. |
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