Constraints on cosmic birefringence using E-mode polarisation

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. 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° with 3σ 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.