Probing CPT Violation with CMB Polarization Measurements
  The electrodynamics modified by the Chern-Simons term $\mathcal{L}_{cs}\sim
p_{\mu}A_{\nu}\tilde F^{\mu\nu}$ with a non-vanishing $p_{\mu}$ violates the
{\it Charge-Parity-Time Reversal} symmetry (CPT) and rotates the linear
polarizations of the propagating {\it Cosmic Microwave Background} (CMB)
photons. In this paper we measure the rotation angle $\Delta\alpha$ by
performing a global analysis on the current CMB polarization measurements from
the {\it seven-year Wilkinson Microwave Anisotropy Probe} (WMAP7), {\it
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 WMAP7, B03 and BICEP all are consistent and their combination gives
$\Delta\alpha=-2.33\pm0.72~{\rm deg}~(68\%~C.L.)$, indicating a $3\,\sigma$
detection of the CPT violation. The QUaD data alone gives
$\Delta\alpha=0.59\pm0.42~{\rm deg}~(68\%~C.L.)$ which has an opposite sign for
the central value and smaller error bar compared to that obtained from WMAP7,
B03 and BICEP. When combining all the polarization data together, we find
$\Delta\alpha=-0.04\pm0.35~{\rm deg}~(68\%~C.L.)$ which significantly improves
the previous constraint on $\Delta\alpha$ and test the validity of the
fundamental CPT symmetry at a higher level.
