Frequency-dependent constraints on cosmic birefringence from the LFI and HFI Planck Data Release 4

Institute of Theoretical Astrophysics, University of Oslo, PO Box 1029 Blindern, 0315 Oslo, Norway
e-mail: j.r.eskilt@astro.uio.no

Received: 4 February 2022
Accepted: 14 April 2022

Abstract

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, β_ν = β, while Faraday rotation from local magnetic fields and Lorentz violating theories predict a cosmic birefringence angle that is proportional to the frequency, ν, to the power of some integer n, β_ν ∝ νⁿ. In this work, we first sampled β_ν individually for each polarized HFI frequency band in addition to the 70 GHz channel from the LFI. We also constrained a power law formula for the birefringence angle, β_ν = β₀(ν/ν₀)ⁿ, with ν₀ = 150 GHz. For a nearly full-sky measurement, f_sky = 0.93, we find β₀ = 0.26° ±0.11° (68% C.L.) and n = −0.45_−0.82^+0.61 when we ignore the intrinsic EB correlations of the polarized foreground emission, and β₀ = 0.33° ±0.12° and n = −0.37_−0.64^+0.49 when we use a filamentary dust model for the foreground EB. Next, we used all the polarized Planck maps, including the 30 and 44 GHz frequency bands. These bands have a negligible foreground contribution from polarized dust emission and we thus treated them separately. Without any modeling of the intrinsic EB of the foreground, we generally find that the inclusion of the 30 and 44 GHz frequency bands raises the measured values of β_ν and tightens n. At nearly full-sky, we measure β₀ = 0.29°_−0.11°^+0.10° and n = −0.35_−0.47^+0.48. Assuming no frequency dependence, we measure β = 0.33° ±0.10°. If our measurements have effectively mitigated the EB of the foreground, our constraints are consistent with a mostly frequency-independent signal of cosmic birefringence.