Strict Limit On Cpt Violation From Polarization Of Gamma-Ray Bursts

We report the strictest observational verification of CPT invariance in the photon sector, as a result of gamma-ray polarization measurement of distant gamma-ray bursts (GRBs), which are the brightest stellar-sized explosions in the Universe. We detected gamma-ray polarization of three GRBs with high significance levels, and the source distances may be constrained by a well-known luminosity indicator for GRBs. For the Lorentz- and CPT-violating dispersion relation E-+(2) = p(2) +/- 2 xi p(3)/M-Pl, where +/- denotes different circular polarization states of the photon, the parameter xi is constrained as vertical bar xi vertical bar < O(10(-15)). Barring precise cancellation between quantum gravity effects and dark energy effects, the stringent limit on the CPT-violating effect leads to the expectation that quantum gravity presumably respects the CPT invariance. DOI: 10.1103/PhysRevLett.109.241104