New two-sided bound on the isotropic Lorentz-violating parameter of modified Maxwell theory

Abstract

There is a unique Lorentz-violating modification of the Maxwell theory of photons, which maintains gauge invariance, CPT, and renormalizability. Restricting the modified-Maxwell theory to the isotropic sector and adding a standard spin-1 2 Dirac particle p ± with minimal coupling to the nonstandard photon γ, the resulting modified-quantum-electrodynamics model involves a single dimensionless "deformation parameter," κ tr . The exact tree-level decay rates for two processes have been calculated: vacuum Cherenkov radiation p ± → p ± γ for the case of positive κ tr and photon decay γ → p + p − for the case of negative κ tr . From the inferred absence of these decays for a particular high-quality ultrahigh-energy-cosmic-ray event detected at the Pierre Auger Observatory and a well-established excess of TeV gamma-ray events observed by the High Energy Stereoscopic System telescopes, a two-sided bound on κ tr is obtained, which improves by eight orders of magnitude upon the best direct laboratory bound. The implications of this result are briefly discussed.

Restrictions from Lorentz invariance violation on cosmic ray propagation

“…The dashed (red) lines are our derived limits from H.E.S.S. and HEGRA reported data [24,31,42,43]. The (colored) bars are the uncertainty of the highest photon energy reported.…”

“…This process is commonly called vacuum Cherenkov radiation (See for instance [20,21,31,33,35]). In a general scenario, the derived physics will be spin dependent, and thus, either particles with spin 0 or 1/2 will be able to emit photons.…”

“…However, the following ansatz, used in Ref. [31], reduces the number of independent parameters from 19 to 1.…”

“…On the analysis regarding this sector, it is usual not to assume the simultaneous presence of LIV corrections for fermions and we are going to do so in our own study along the following sections. The CPT-even term can be studied separately as in the so called modified Maxwell theory (modM [31]),…”

“…Following Refs. [31,33], the dispersion relations for a single photon from modM and MCS models are written as…”