Test of Lorentz invariance: exploiting the potential of air showers at ultra-high energy

• Applicant: Professor Dr. Markus Risse
• Subject Area: Nuclear and Elementary Particle Physics, Quantum Mechanics, Relativity, Fields ; Astrophysics and Astronomy
• Term: since 2018
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 408049454

As a fundamental pillar of modern physics, Lorentz invariance is a key target of experimental precision tests. This holds even more since Lorentz invariance may actually be violated at some level as suggested by theoretical considerations when trying to combine general relativity and quantum mechanics. The discovery of a violation of Lorentz invariance (LV) would constitute an essential breakthrough in fundamental physics; confirming the validity of Lorentz invariance with improving accuracy gives important guidance towards a more fundamental theory. Some of the world-best tests of Lorentz invariance in the photon sector make use of astroparticles such as cosmic rays. The photon sector allows for clean probes of LV physics, and cosmic rays reach ultra-high energies (UHE) far beyond the capabilities of current technology. Within the framework of modified Maxwell theory and regarding extensive air showers initiated by UHE cosmic rays, limits were obtained that significantly improved previous ones. This was based on including the new LV processes of photon decay and vacuum Cherenkov radiation - both are forbidden in standard physics - in the shower simulation and comparing the expectations to data. So far, the analysis was restricted to the depth of shower maximum as an observable, a quantity from the longitudinal shower profile. The number of shower muons on ground provides additional information. In particular, the correlation between shower maximum and muon number is closely related to the purity of the cosmic-ray beam. Measurements of this quantity exist, with the ground signal as a proxy to muon number. In the renewal project, the analysis will be extended to include this correlation as an additional observable. This requires the implementation of the LV processes in the full three-dimensional shower simulation code. The analysis will also be updated with newest air shower data. A gain in sensitivity to LV by about two orders of magnitude is expected within the project. With the full shower simulations at hand, also the general impact of the LV effects on ground particle distributions will be examined in detail.

• DFG Programme: Research Grants