Bounds on Lorentz invariance violation from muon fluctuations at the Pierre Auger Observatory

TL;DR

This paper uses muon fluctuation data from the Pierre Auger Observatory to set new, strong bounds on Lorentz invariance violation, exploring a novel observable in ultra-high-energy cosmic ray interactions.

Contribution

It introduces muon number fluctuations as a new observable to constrain Lorentz invariance violations in cosmic ray air showers, providing the strongest bounds in the hadronic sector.

Findings

Established the strongest bounds on Lorentz invariance violation in the hadronic sector.

Demonstrated muon fluctuations as a powerful new observable for fundamental physics.

Constraints do not depend on cosmic ray mass composition assumptions.

Abstract

Quantum gravity theories often modify spacetime symmetries. In particular, Lorentz invariance may be violated when approaching the Planck scale. Although the scales at which interactions occur in extensive air showers induced by ultra-high-energy cosmic rays in the atmosphere are many orders of magnitude below the Planck scale, these violations might still be observable. In this work, the fluctuations in the number of muons in the extensive air showers measured at the Pierre Auger Observatory are exploited, for the first time, to constrain Lorentz invariance violations. The bounds derived in the hadronic sector are the strongest ever obtained, and do not rely on assumptions about the mass composition of ultra-high-energy cosmic rays. The fluctuations in the number of muons constitute a new and powerful observable to further explore Lorentz invariance in a region of the parameter space not accessible to other observables.