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Recent limits on Lorentz invariance violation using gamma rays
Some candidates for the theory of quantum gravity predict a violation or deformation of the Lorentz symmetry. The phenomenon, known as Lorentz invariance violation (LIV), suggests that the speed of photons depends on their energy. A simple way to parametrize this effect is to introduce an energy-dependent correction to the photon dispersion relation. This tiny effect might be accumulated for very high energy (VHE, E > 100 GeV) photons crossing cosmological distances. As a result, the time-of-flight (ToF) of photons of different energies, presumably emitted simultaneously at the source, would be different. We use MAGIC telescopes data to test this hypothesis on VHE gamma rays emitted by variable astronomical sources. On January 14, 2019, the MAGIC telescopes detected GRB 190114C at teraelectronvolt energies, recording the most energetic photons ever observed from a gamma-ray burst. This unique observation presented an ideal opportunity to probe energy dependence of the speed of light in vacuo. Based on a set of well-justified assumptions on the possible intrinsic spectral and temporal evolution, we obtained competitive lower limits on the quadratic leading order modification of the speed of light. This is the first LIV test ever performed on a gamma-ray burst signal at TeV energies and will serve as a stepping stone to future studies. The results will be put into context of the most stringent bounds on LIV obtained using gamma rays.