Tomographic constraint on anisotropic cosmic birefringence

TL;DR

This paper uses Planck PR4 polarization data to set the first constraints on anisotropic cosmic birefringence generated during reionization, finding results consistent with null and discussing future prospects for more sensitive measurements.

Contribution

It introduces estimators for anisotropic cosmic birefringence at different redshifts and applies them to Planck data to constrain models of birefringence during reionization.

Findings

Power spectrum consistent with null hypothesis

Model by Ferreira et al. (2024) remains compatible with data

Future experiments will improve constraints

Abstract

We constrain anisotropic cosmic birefringence generated at reionization using Planck PR4 polarization data for the first time. Several recent analyses of WMAP and Planck polarization data have found a tantalizing hint of isotropic cosmic birefringence. Ongoing and future CMB experiments will test isotropic cosmic birefringence by improving the absolute angle calibration and understanding the intrinsic parity-odd power spectrum of the Galactic foregrounds. Alternatively, measuring anisotropies in cosmic birefringence and its time evolution is also a key observable to confirm the signal of cosmic birefringence and to investigate its origin. We discuss estimators of anisotropic cosmic birefringence generated at different redshifts. We then estimate anisotropic cosmic birefringence generated at reionization from the PR4 data, showing that the power spectrum is consistent with null. We find that the model proposed by Ferreira et al. (2024) is still consistent with the observation. Future full-sky CMB experiments such as LiteBIRD and PICO will help tighten the tomographic constraint to test models of cosmic birefringence.