New limits on Planck scale Lorentz violation in QED

Abstract

Constraints on possible Lorentz symmetry violation (LV) of order E/M_Planck for electrons and photons in the framework of effective field theory (EFT) are discussed. Using (i) the report of polarized MeV emission from GRB021206 and (ii) the absence of vacuum Čerenkov radiation from synchrotron electrons in the Crab nebula, we improve previous bounds by 10^-10 and 10^-2 respectively. We also show that the LV parameters for positrons and electrons are different, discuss electron helicity decay, and investigate investigate how prior constraints are modified by the relations between LV parameters implied by EFT.

4 pages; figure replaced; reference added, typo fixed; (v4): added caveat concerning observation of GRB polarization, weakened birefringence bound by factor of ten (due to previous computational error), added references, editorial changes in presentation; v5: Possible role of positrons in producing Crab radiation and effect on constraints noted, reference added, minor editorial changes. Essentially the version published in PRL