Astroparticle-physics search for Lorentz violation in the photon sector

• Applicants: Professor Dr. Frans R. Klinkhamer; Professor Dr. Markus Risse
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields
• Term: from 2012 to 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 221244986

Spacetime is dynamic and quantum mechanics inherently random. This suggests that space may not be perfectly smooth at very small length scales and that Lorentz invariance may be fundamentally violated. An ideal testing ground of Lorentz invariance is the photon sector. There are 19 dimensionless parameters, of which 10 lead to vacuum birefringence and are already constrained at the 10-32 level. The most urgent task is to bound the remaining 9 parameters of the nonbirefringent modified Maxwell theory. Of these 9 parameters, the single isotropic parameter is the most difficult to bound or determine in the laboratory. The best indirect bounds were obtained by the applicants from ultra-high-energy cosmic rays (Pierre Auger Observatory) and TeV gamma-rays (H.E.S.S.). This project aims at improving these bounds by at least two orders of magnitude which is especially important for the isotropic parameter. On the experimental side, this requires the construction of an appropriate Auger data sample. On the theoretical side, the energy-threshold conditions must be refined to incorporate the fact that the proton, for example, is not a point particle. In addition, there is always the possibility of discovery of Lorentz-violating effects. For this reason, a significant part of this project is devoted to search strategies and a preliminary scan of the available data from Auger. Both the detection of Lorentz violation in the photon sector and the extraction of extremely tight upper bounds would be of importance to physics as a whole, but in a different way, of course.

• DFG Programme: Research Grants