New Constraints on Quantum Gravity from XRay and GammaRay Observations
Abstract
One aspect of the quantum nature of spacetime is its “foaminess” at very small scales. Many models for spacetime foam are defined by the accumulation power α, which parameterizes the rate at which Planckscale spatial uncertainties (and the phase shifts they produce) may accumulate over large path lengths. Here α is defined by the expression for the pathlength fluctuations, δ \ell , of a source at distance ℓ, wherein δ \ell ≃ {{\ell }^{1α }}\ell _{P}^{α }, with {{\ell }_{P}} being the Planck length. We reassess previous proposals to use astronomical observations of distant quasars and active galactic nuclei to test models of spacetime foam. We show explicitly how wavefront distortions on small scales cause the image intensity to decay to the point where distant objects become undetectable when the pathlength fluctuations become comparable to the wavelength of the radiation. We use Xray observations from Chandra to set the constraint α ≳ 0.58, which rules out the randomwalk model (with α =1/2). Much firmer constraints can be set by utilizing detections of quasars at GeV energies with Fermi and at TeV energies with groundbased Cerenkov telescopes: α ≳ 0.67 and α ≳ 0.72, respectively. These limits on α seem to rule out α =2/3, the model of some physical interest.
 Publication:

The Astrophysical Journal
 Pub Date:
 May 2015
 DOI:
 10.1088/0004637X/805/1/10
 arXiv:
 arXiv:1411.7262
 Bibcode:
 2015ApJ...805...10P
 Keywords:

 cosmology: theory;
 elementary particles;
 gravitation;
 methods: data analysis;
 methods: statistical;
 quasars: general;
 Astrophysics  Cosmology and Nongalactic Astrophysics;
 Astrophysics  High Energy Astrophysical Phenomena;
 General Relativity and Quantum Cosmology
 EPrint:
 11 pages, 9 figures, ApJ, in press