Probing CPT violation with CMB polarization measurements

The electrodynamics modified by the Chern-Simons term Lcs∼pμAνF˜μν with a non-vanishing pμ violates the Charge-Parity-Time Reversal symmetry (CPT) and rotates the linear polarizations of the propagating Cosmic Microwave Background (CMB) photons. In this Letter we measure the rotation angle Δα by performing a global analysis on the current CMB polarization measurements from the five-year Wilkinson Microwave Anisotropy Probe (WMAP5), BOOMERanG 2003 (B03), BICEP and QUaD using a Markov Chain Monte Carlo method. Neglecting the systematic errors of these experiments, we find that the results from WMAP5, B03 and BICEP all are consistent and their combination gives Δα=−2.62±0.87deg (68% C.L.), indicating a 3σ detection of the CPT violation. The QUaD data alone gives Δα=0.59±0.42deg (68% C.L.) which has an opposite sign for the central value and smaller error bar compared to that obtained from WMAP5, B03 and BICEP. When combining all the polarization data together, we find Δα=0.09±0.36deg (68% C.L.) which significantly improves the previous constraint on Δα and test the validity of the fundamental CPT symmetry at a higher level.