Detailed study of HWP non-idealities and their impact on future measurements of CMB polarization anisotropies from space

Abstract

We study the propagation of a specific class of instrumental systematics to the reconstruction of the B-mode power spectrum of the cosmic microwave background (CMB). We focus on non-idealities of the half-wave plate (HWP), a polarization modulator that will be deployed by future CMB experiments, such as the phase-A satellite mission LiteBIRD. More in details, we study the effects of non-ideal HWP properties, such as transmittance, phase shift and cross-polarization. To this purpose, we develop a simple, yet stand-alone end-to-end simulation pipeline adapted to LiteBIRD. Through the latter, we analyze the effects of a possible mismatch between the measured frequency profiles of HWP properties (used in the mapmaking stage of the pipeline) and the actual profiles (used in the sky-scanning step). We simulate single-frequency, CMB-only observations to emphasize the effects of non-idealities on the BB power spectrum. We also consider multi-frequency observations to account for the frequency dependence of HWP properties and the contribution of foreground emission. We quantify the systematics effects in terms of a bias ∆r on the tensor-toscalar ratio r with respect to the ideal case of no-systematics. We derive the accuracy requirements on the measurements of HWP properties by requiring ∆r < 10 −5 (1% of the expected LiteBIRD sensitivity on r). The analysis is introduced by a detailed presentation of the mathematical formalism employed in this work, including the use of the Jones and Mueller matrix representations.