Searching for CPT Violation with Cosmic Microwave Background Data from WMAP and BOOMERANG

We search for signatures of Lorentz and CPT violations in the cosmic microwave background (CMB) temperature and polarization anisotropies by using the Wilkinson Microwave Anisotropy Probe (WMAP) and the 2003 flight of BOOMERANG (B03) data. We note that if the Lorentz and CPT symmetries are broken by a Chern-Simons term in the effective Lagrangian, which couples the dual electromagnetic field strength tensor to an external four-vector, the polarization vectors of propagating CMB photons will get rotated. Using the WMAP data alone, one could put an interesting constraint on the size of such a term. Combined with the B03 data, we found that a nonzero rotation angle of the photons is mildly favored: Δα=-6.0(+4.0)/(-4.0)(+3.9)/(-3.7)deg⁡(1,2σ).