Imaging parity-violation in the CMB

TL;DR

This paper introduces a local, robust estimator for detecting parity-violating modes in the CMB polarization, applying it to Planck data to constrain polarization rotation and map direction-dependent effects.

Contribution

It develops a novel peak stacking method based on polarization correlations to detect parity violation in the CMB, effective with partial-sky data.

Findings

Constraint on polarization rotation angle: < 0.72 degrees at 95% confidence.

Demonstrated local reconstruction of direction-dependent rotation maps.

Applied the method successfully to Planck data.

Abstract

Correlations of polarization components in the coordinate frame are a natural basis for searches of parity-violating modes in the Cosmic Microwave Background (CMB). This fact can be exploited to build estimators of parity-violating modes that are {\sl 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 {\sl Planck} maps and obtain a constraint on the monopole of the polarization rotation angle $\alpha < 0.72$ degrees at $95\%$ We also demonstrate how the tool can be used as a local method for reconstructing maps of direction dependent rotation $\alpha(\hat {n})$.