Improved limit on quantum-spacetime modifications of Lorentz symmetry from observations of gamma-ray blazars

TL;DR

This paper improves constraints on quantum-spacetime effects on Lorentz symmetry by analyzing gamma-ray observations from blazars, showing current data can approach Planck-scale sensitivity and clarifying theoretical limitations.

Contribution

It provides an enhanced limit on quantum-gravity modifications of Lorentz symmetry using recent gamma-ray absorption data and clarifies misconceptions about photon decay predictions.

Findings

New limit approaches Planck-scale sensitivity.

Photon decay into electron-positron pairs is not allowed in the tested theory.

Limitations of phenomenological models are discussed.

Abstract

In the quantum-gravity literature there has been interest in the possibility that quantum properties of spacetime might affect the energy/momentum dispersion relation. The most used test theory for data analysis is based on a modification of the laws of propagation proposed in astro-ph/9712103 [Nature 393,763], and the present best limit on the quantum-gravity scale was obtained in gr-qc/9810044 [Phys.Rev.Lett.83,2108]. I derive an improved limit using recent experimental information on absorption by the infrared diffuse extragalactic background of $\gamma$-rays emitted by blazars. Foreseeable more accurate determinations of the absorption levels could achieve Planck-scale sensitivity. As a corollary I also show that, contrary to the recent claim of astro-ph/0208507v3, the test theory here considered does not allow decays of photons into electron-positron pairs, and I expose the limitations of phenomenological proposals, such as the one reported in astro-ph/0212190, in which one attempts to infer limits on the kinematic theory here considered through the ad hoc introduction of a dynamical framework.