High precision simulations of weak lensing effect on Cosmic Microwave Background polarization

TL;DR

This paper develops a semi-analytic framework and a high-performance code for precise, robust pixel-domain simulations of gravitational lensing effects on the CMB, focusing on B-mode polarization.

Contribution

It introduces a semi-analytic method to optimize simulation parameters and presents lenS2HAT, a scalable code enabling high-resolution lensing simulations of the CMB.

Findings

Achieved high-precision lensing simulations at large data volumes

Validated the semi-analytic framework with extensive numerical results

Provided publicly available code for the community

Abstract

We study accuracy, robustness and self-consistency of pixel-domain simulations of the gravitational lensing effect on the primordial CMB anisotropies due to the large-scale structure of the Universe. In particular, we investigate dependence of the results precision on some crucial parameters of such techniques and propose a semi-analytic framework to determine their values so the required precision is a priori assured and the numerical workload simultaneously optimized. Our focus is on the B-mode signal but we discuss also other CMB observables, such as total intensity, T, and E-mode polarization, emphasizing differences and similarities between all these cases. Our semi-analytic considerations are backed up by extensive numerical results. Those are obtained using a code, nicknamed lenS2HAT -- for Lensing using Scalable Spherical Harmonic Transforms (S2HAT) -- which we have developed in the course of this work. The code implements a version of the pixel-domain approach of Lewis (2005) and permits performing the simulations at very high resolutions and data volumes, thanks to its efficient parallelization provided by the S2HAT library -- a parallel library for a calculation of the spherical harmonic transforms. The code is made publicly available.