* Astronomy

Title: Lorentz Invariance Violation and the Observed Spectrum of Ultrahigh Energy Cosmic Rays
Authors: S. T. Scully (JMU), F. W. Stecker (NASA/GSFC)
(Version v3)

There has been much interest in possible violations of Lorentz invariance, particularly motivated by quantum gravity theories. It has been suggested that a small amount of Lorentz invariance violation (LIV) could turn off photomeson interactions of ultrahigh energy cosmic rays (UHECRs) with photons of the cosmic background radiation and thereby eliminate the resulting sharp steepening in the spectrum of the highest energy CRs predicted by Greisen Zatsepin and Kuzmin (GZK). Recent measurements of the UHECR spectrum reported by the HiRes and Auger collaborations, however, indicate the presence of the GZK effect. We present the results of a detailed calculation of the modification of the UHECR spectrum caused by LIV using the formalism of Coleman and Glashow. We then compare these results with the experimental UHECR data from Auger and HiRes. Based on these data, we find a best fit amount of LIV of 4.5^{+1.5}_{-4.5} x  10^{-23},consistent with an upper limit of 6 x 10^{-23}. This possible amount of LIV can lead to a recovery of the cosmic ray spectrum at higher energies than presently observed. Such an LIV recovery effect can be tested observationally using future detectors.

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Physicists at Indiana University have developed a promising new way to identify a possible abnormality in a fundamental building block of Einstein's theory of relativity known as "Lorentz invariance." If confirmed, the abnormality would disprove the basic tenet that the laws of physics remain the same for any two objects travelling at a constant speed or rotated relative to one another.
IU distinguished physics professor Alan Kostelecky and graduate student Jay Tasson take on the long-held notion of the exact symmetry promulgated in Einstein's 1905 theory and show in a paper to be published in the Jan. 9 issue of Physical Review Letters that there may be unexpected violations of Lorentz invariance that can be detected in specialised experiments.

"It is surprising and delightful that comparatively large relativity violations could still be awaiting discovery despite a century of precision testing. Discovering them would be like finding a camel in a haystack instead of a needle" - Alan Kostelecky.

If the findings help reveal the first evidence of Lorentz violations, it would prove relativity is not exact. Space-time would not look the same in all directions and there would be measurable relativity violations, however minuscule.

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Title: Prospects for Large Relativity Violations in Matter-Gravity Couplings
Authors: V. Alan Kostelecký and Jay D. Tasson

Deviations from relativity are tightly constrained by numerous experiments. A class of unmeasured and potentially large violations is presented that can be tested in the laboratory only via weak-gravity couplings. Specialised highly sensitive experiments could achieve measurements of the corresponding effects. A single constraint of 1 x 10^-11 GeV is extracted on one combination of the 12 possible effects in ordinary matter. Estimates are provided for attainable sensitivities in existing and future experiments.

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