http://arxiv.org/abs/2201.13347

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. For a nearly full-sky measurement, $f_{\text{sky}}=0.93$, we find $\beta_0 = 0.26^{\circ}\pm0.11^\circ$ $(68\% \text{ C.L.})$ and $n=-0.45^{+0.61}{-0.82}$ when we ignore the intrinsic $EB$ correlations of the polarized foreground emission, and $\beta_0 = 0.33^\circ \pm 0.12^\circ$ and $n=-0.37^{+0.49}{-0.64}$ when we use a filamentary dust model for the foreground $EB$. Next, we use all the polarized Planck maps, including the 30 and 44 GHz frequency bands. These bands have a negligible foreground contribution from polarized dust emission. We, therefore, treat 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 $\beta_\nu$ and tightens $n$. At nearly full-sky, we measure $\beta_0=0.29^{\circ+0.10^\circ}{\phantom{\circ}-0.11^\circ}$ and $n=-0.35^{+0.48}{-0.47}$. Assuming no frequency dependence, we measure $\beta=0.33^\circ \pm 0.10^\circ$. If our measurements have effectively mitigated the $EB$ of the foreground, our constraints are consistent with a mostly frequency-independent signal of cosmic birefringence.

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J. Eskilt
Tue, 1 Feb 22
46/73

Comments: 11 pages, 9 figures, 3 tables. Submitted to A&A