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

¹ Dipartimento di Fisica e Scienze della Terra, Università di Ferrara, Polo Scientifico e Tecnologico, Edificio C Via Saragat, 1, 44122 Ferrara, Italy
e-mail: serena.giardiello@unife.it
² Istituto Nazionale di Fisica Nucleare, sezione di Ferrara, Polo Scientifico e Tecnologico, Edificio C Via Saragat, 1, 44122 Ferrara, Italy
³ Université de Paris, CNRS, Astroparticule et Cosmologie, 75006 Paris, France
⁴ Istituto Nazionale di Astrofisica, Osservatorio di Astrofisica e Scienza dello Spazio di Bologna, Via Gobetti 101, 40129 Bologna, Italy
⁵ Istituto Nazionale di Fisica Nucleare, Sezione di Bologna, Viale Berti Pichat 6/2, 40127 Bologna, Italy
⁶ Department of Physics, Okayama University, 3-1-1 Tsushimanaka Kita-ku, Okayama 700-8530, Japan
⁷ Dipartimento di Fisica, Sapienza Università di Roma, sezione di Roma1, P.le A. Moro 5, 00185 Roma, Italy
⁸ Istituto Nazionale di Fisica Nucleare, sezione di Roma1, P.le A. Moro 5, 00185 Roma, Italy

Received: 23 June 2021
Accepted: 24 October 2021

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 the non-idealities of the half-wave plate (HWP), a polarization modulator that is to be deployed by future CMB experiments, such as the phase-A satellite mission LiteBIRD. We study the effects of non-ideal HWP properties, such as transmittance, phase shift, and cross-polarization. To this end, we developed a simple, yet stand-alone end-to-end simulation pipeline adapted to LiteBIRD. We analyzed 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 simulated single-frequency, CMB-only observations to emphasize the effects of non-idealities on the BB power spectrum. We also considered multi-frequency observations to account for the frequency dependence of HWP properties and the contribution of foreground emission. We quantified the systematic effects in terms of a bias Δr on the tensor-to-scalar ratio, r, with respect to the ideal case without systematic effects. We derived the accuracy requirements on the measurements of HWP properties by requiring Δr < 10⁻⁵ (1% of the expected LiteBIRD sensitivity on r). Our 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.