Parity violation constraints using 2006-2007 QUaD CMB polarization   spectra
  We constrain parity-violating interactions to the surface of last scattering using spectra from the QUaD experiment's second and third seasons of observations by searching for a possible systematic rotation of the polarization directions of CMB photons. We measure the rotation angle due to such a possible "cosmological birefringence" to be 0.55 deg. +/- 0.82 deg. (random) +/- 0.5 deg. (systematic) using QUaD's 100 and 150 GHz TB and EB spectra over the multipole range 200 < l < 2000, consistent with null, and constrain Lorentz violating interactions to < 2^-43 GeV (68% confidence limit). This is the best constraint to date on electrodynamic parity violation on cosmological scales. 
QUaD Collaboration: E. Y. S. Wu (1), P. Ade (2), J. Bock (3 and 4), M.   Bowden (1 and 5), M. L. Brown (6), G. Cahill (7), P...