Constraints on cosmic birefringence using $E$-mode polarisation

TL;DR

This paper proposes an independent method using temperature and E-mode polarization data to constrain cosmic birefringence, offering a way to verify B-mode based measurements and mitigate calibration degeneracies.

Contribution

It introduces a novel approach to measure cosmic birefringence using only temperature and E-mode polarization, reducing reliance on B-mode data.

Findings

Potential to constrain birefringence angle to 0.3° at 3σ significance with ideal data.

Method is less affected by polarisation miscalibration issues.

Provides a complementary check for B-mode based birefringence measurements.

Abstract

A birefringent universe could show itself through a rotation of the plane of polarisation of the cosmic microwave background photons. This is usually investigated using polarisation $B$ modes, which is degenerate with miscalibration of the orientation of the polarimeters. Here we point out an independent method for extracting the birefringence angle using only temperature and $E$-mode signals. We forecast that, with an ideal cosmic-variance-limited experiment, we could constrain a birefringence angle of $0.3^\circ$ with $3\,\sigma$ statistical significance, which is close to the current constraints using $B$ modes. We explore how this method is affected by the systematic errors introduced by the polarisation efficiency. In the future, this could provide an additional way of checking any claimed $B$-mode derived birefringence signature.