Probing frequency-dependent half-wave plate systematics for CMB experiments with full-sky beam convolution simulations

TL;DR

This paper investigates how frequency-dependent systematics of half-wave plates affect CMB polarization measurements, using advanced full-sky simulations that incorporate realistic beam effects and HWP non-idealities, highlighting potential biases in primordial B-mode detection.

Contribution

It presents the first time-domain simulations combining HWP non-idealities with full-sky beam convolution, revealing impacts on polarization angle offsets and B-mode residuals in CMB experiments.

Findings

Achromatic HWP configurations cause polarization angle biases.

Beam cross-polarization and sidelobes significantly affect B-mode residuals.

Simulations highlight the need for detailed modeling of HWP effects in CMB analysis.

Abstract

We study systematic effects from half-wave plates (HWPs) for cosmic microwave background (CMB) experiments using full-sky time-domain beam convolution simulations. Using an optical model for a fiducial spaceborne two-lens refractor telescope, we investigate how different HWP configurations optimized for dichroic detectors centred at 95 and 150 GHz impact the reconstruction of primordial B-mode polarization. We pay particular attention to possible biases arising from the interaction of frequency dependent HWP non-idealities with polarized Galactic dust emission and the interaction between the HWP and the instrumental beam. To produce these simulations, we have extended the capabilities of the publicly available beamconv code. To our knowledge, we produce the first time-domain simulations that include both HWP non-idealities and realistic full-sky beam convolution. Our analysis shows how certain achromatic HWP configurations produce significant systematic polarization angle offsets that vary for sky components with different frequency dependence. Our analysis also demonstrates that once we account for interactions with HWPs, realistic beam models with non-negligible cross-polarization and sidelobes will cause significant B-mode residuals that will have to be extensively modelled in some cases.