IMAGING PARITY-VIOLATING MODES IN THE CMB

Correlations of polarization components in the coordinate frame are a natural basis for searches of parity-violating modes in the cosmic microwave background. This fact can be exploited to build estimators of parity-violating modes that are local and robust with respect to partial-sky coverage or inhomogeneous weighting. As an example application of a method based on these ideas, we develop a peak stacking tool that isolates the signature of parity-violating modes. We apply the tool to Planck maps and obtain a constraint on the monopole of the polarization rotation angle alpha < 0.degrees 72 at 95% We also demonstrate how the tool can be used as a local method for reconstructing maps of direction dependent rotation alpha (<(n)over cap>).