How to De-Rotate the Cosmic Microwave Background Polarization

TL;DR

This paper presents a method to detect and map frequency-independent polarization rotation in the CMB, enabling differentiation between primordial B modes and those caused by rotation effects.

Contribution

It introduces a technique using higher-order correlations to reconstruct the rotation angle across the sky, distinguishing it from cosmic shear effects.

Findings

Reconstruction of rotation angle from polarization correlations.

Method to differentiate primordial B modes from rotation-induced B modes.

Geometric distinction between rotation effects and cosmic shear.

Abstract

If the linear polarization of the cosmic microwave background (CMB) is rotated in a frequency-independent manner as it propagates from the surface of last scatter, it may introduce a B-mode polarization. Here I show that measurement of higher-order TE, EE, EB, and TB correlations induced by this rotation can be used to reconstruct the rotation angle as a function of position on the sky. This technique can be used to distinguish primordial B modes from those induced by rotation. The effects of rotation can be distinguished geometrically from similar effects due to cosmic shear.