Probes of Lorentz Violation
  Lorentz invariance is such an important principle of fundamental physics that it should constantly be subjected to experimental scrutiny as well as theoretical questioning. Distant astrophysical sources of energetic photons with rapid time variations, such as active galactic nuclei (AGNs) and gamma-ray bursters (GRBs), provide ideal experimental opportunities for testing Lorentz invariance. The Cherenkov Telescope Array (CTA) is an excellent experimental tool for making such tests with sensitivities exceeding those possible using other detectors. 
John Ellis and Nick E. Mavromatos
astro-ph.HE astro-ph.CO gr-qc hep-ex hep-ph