Tomographic constraint on anisotropic cosmic birefringence

Understand

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.