Lensing corrections on galaxy-lensing cross correlations and galaxy-galaxy auto correlations

TL;DR

This paper assesses the significance of lensing corrections on galaxy-lensing cross correlations and galaxy auto correlations, finding they are generally small but potentially important for future high-precision measurements.

Contribution

It provides a detailed evaluation of lensing corrections for cross correlations without the Limber approximation, highlighting the need to consider additional Jacobian terms.

Findings

Lensing corrections are small for high signal-to-noise correlations.

The size of corrections depends on redshift distributions.

Additional Jacobian terms may be significant and require further study.

Abstract

We study the impact of lensing corrections on modeling cross correlations between CMB lensing and galaxies, cosmic shear and galaxies, and galaxies in different redshift bins. Estimating the importance of these corrections becomes necessary in the light of anticipated high-accuracy measurements of these observables. While higher order lensing corrections (sometimes also referred to as post Born corrections) have been shown to be negligibly small for lensing auto correlations, they have not been studied for cross correlations. We evaluate the contributing four-point functions without making use of the Limber approximation and compute line-of-sight integrals with the numerically stable and fast FFTlog formalism. We find that the relative size of lensing corrections depends on the respective redshift distributions of the lensing sources and galaxies, but that they are generally small for high signal-to-noise correlations. We point out that a full assessment and judgement of the importance of these corrections requires the inclusion of lensing Jacobian terms on the galaxy side. We identify these additional correction terms, but do not evaluate them due to their large number. We argue that they could be potentially important and suggest that their size should be measured in the future with ray-traced simulations. We make our code publicly available.