Frequency-Dependent Constraints on Cosmic Birefringence from the LFI and HFI Planck Data Release 4

Understand

We present new constraints on the frequency dependence of the cosmic birefringence angle from the Planck data release 4 polarization maps.

• An axion field coupled to electromagnetism predicts a nearly frequency-independent birefringence angle, $\beta_\nu = \beta$, while Faraday rotation from local magnetic fields and Lorentz violating theories predict a cosmic birefringence angle that is proportional to the frequency, $\nu$, to the power of some integer $n$, $\beta_\nu \propto \nu^n$.
• In this work, we first sample $\beta_\nu$ individually for each polarized HFI frequency band in addition to the 70 GHz channel from the LFI.
• We also constrain a power-law formula for the birefringence angle, $\beta_\nu=\beta_0(\nu/\nu_0)^n$, with $\nu_0 = 150$ GHz.