Robustness of cosmic birefringence measurement against Galactic foreground emission and instrumental systematics

TL;DR

This study assesses the robustness of cosmic birefringence measurements against Galactic foregrounds and instrumental systematics using realistic simulations, proposing methods to correct foreground-induced biases for future high-precision CMB analyses.

Contribution

It demonstrates the robustness of birefringence measurement techniques against many systematic effects and introduces a Bayesian template-based correction for dust foreground biases.

Findings

Method is robust against polarization angle miscalibration.

Systematics like beam leakage have minimal impact.

Dust EB correlation can bias measurements, requiring modeling corrections.

Abstract

The polarization of the cosmic microwave background (CMB) can be used to search for parity-violating processes like that predicted by a Chern-Simons coupling to a light pseudoscalar field. Such an interaction rotates $E$ modes into $B$ modes in the observed CMB signal by an effect known as cosmic birefringence. Even though isotropic birefringence can be confused with the rotation produced by a miscalibration of the detectors' polarization angles the degeneracy between both effects is broken when Galactic foreground emission is used as a calibrator. In this work, we use realistic simulations of the High-Frequency Instrument of the Planck mission to test the impact that Galactic foreground emission and instrumental systematics have on the recent birefringence measurements obtained through this technique. Our results demonstrate the robustness of the methodology against the miscalibration of polarization angles and other systematic effects, like intensity-to-polarization leakage, beam leakage, or cross-polarization effects. However, our estimator is sensitive to the $EB$ correlation of polarized foreground emission. Here we propose to correct the bias induced by dust $EB$ by modeling the foreground signal with templates produced in Bayesian component-separation analyses that fit parametric models to CMB data. Acknowledging the limitations of currently available dust templates like that of the Commander sky model, high-precision CMB data and a characterization of dust beyond the modified blackbody paradigm are needed to obtain a definitive measurement of cosmic birefringence in the future.