[Paper Review] QuickPol: Fast effective beam matrices calculation for CMB polarization

E. Hivon, Sylvain Mottet+1 more|arXiv (Cornell University)|Aug 31, 2016

Superconducting and THz Device Technology34 references3 citations

TL;DR

QuickPol enables fast, accurate computation of full effective beam transfer functions and temperature-to-polarization leakage in CMB polarization experiments, accounting for scanning strategies, beam imperfections, and response mismatches. Validated on Planck-HFI simulations, it efficiently propagates instrumental uncertainties to final power spectra, supporting future experiments with rotating half-wave plates.

ABSTRACT

Current and planned observations of the Cosmic Microwave Background (CMB) polarization anisotropies, with their ever increasing number of detectors, have reached a potential accuracy that requires a very demanding control of systematic effects. While some of these systematics can be reduced in the design of the instruments, others will be have to be modeled and hopefully accounted for or corrected a posteriori. We propose QuickPol, a quick and accurate calculation of the full effective beam transfer function and of temperature to polarization leakage at the power spectra level, as induced by beam imperfections and mismatches between detector optical and electronic responses. All the observation details such as exact scanning strategy, imperfect polarization measurements and flagged samples are accounted for. Our results are validated on Planck-HFI simulations. We show how the pipeline can be used to propagate instrumental uncertainties up to the final science products, and could be applied to experiments with rotating half wave plates.

Motivation & Objective

• To address the growing challenge of systematic effects in high-accuracy CMB polarization observations due to beam imperfections and response mismatches.
• To develop a computationally efficient method for calculating the full effective beam transfer function at the power spectrum level.
• To account for detailed observational factors such as scanning strategies, flagged samples, and imperfect polarization measurements.
• To enable propagation of instrumental uncertainties through to final science products, supporting robust data analysis.

Proposed method

• QuickPol computes the effective beam transfer function by modeling the convolution of detector beam responses with the scanning strategy.
• It incorporates both optical and electronic response mismatches between detectors to quantify temperature-to-polarization leakage.
• The method uses a matrix-based formalism to represent beam responses and their interactions across the sky, enabling fast computation.
• It integrates exact scanning information and flags for bad or flagged samples to ensure realistic simulations.
• The pipeline is designed to handle large detector counts typical of current and future CMB experiments.
• It is validated using Planck-HFI simulations, demonstrating accuracy and computational efficiency.

Experimental results

Research questions

• RQ1 How can beam imperfections and response mismatches be accurately modeled to predict temperature-to-polarization leakage in CMB power spectra?
• RQ2 What is the most efficient computational approach to compute full effective beam transfer functions without sacrificing accuracy?
• RQ3 How do scanning strategies and flagged samples affect the final beam response and leakage in polarization power spectra?
• RQ4 To what extent can instrumental uncertainties be propagated through the pipeline to impact final science results?
• RQ5 Can the method be generalized to experiments using rotating half-wave plates?

Key findings

• QuickPol enables fast and accurate computation of the full effective beam transfer function, including temperature-to-polarization leakage, for CMB polarization experiments.
• The method correctly accounts for scanning strategies, beam asymmetries, and response mismatches between detectors.
• Validation on Planck-HFI simulations confirms the accuracy of the beam transfer function and leakage predictions.
• The pipeline efficiently handles large numbers of detectors, making it suitable for next-generation CMB experiments.
• It successfully propagates instrumental uncertainties up to the final power spectra, supporting robust error budgeting.
• The approach is adaptable to experiments with rotating half-wave plates, extending its applicability to future instrumentation.