Testing the Cosmic Shear Spatially-Flat Universe Approximation with Generalized Lensing and Shear Spectra

TL;DR

This paper introduces GLaSS, a Python code for calculating generalized cosmic shear spectra, and tests the common assumption that spatial flatness can be approximated in universes with slight curvature, finding it negligible for Stage IV experiments.

Contribution

The paper presents GLaSS, a new flexible tool for cosmic shear spectra computation, and evaluates the impact of the spatially-flat universe approximation in curved cosmologies.

Findings

GLaSS is a fast, modular Python tool for cosmic shear spectra.

The spatially-flat universe approximation has negligible impact on Stage IV cosmic shear results.

The code is publicly available for the community.

Abstract

We introduce the Generalised Lensing and Shear Spectra GLaSS code which is available for download from https://github.com/astro-informatics/GLaSS It is a fast and flexible public code, written in Python, that computes generalized spherical cosmic shear spectra. The commonly used tomographic and spherical Bessel lensing spectra come as built-in run-mode options. GLaSS is integrated into the Cosmosis modular cosmological pipeline package. We outline several computational choices that accelerate the computation of cosmic shear power spectra. Using GLaSS, we test whether the assumption that using the lensing and projection kernels for a spatially-flat universe -- in a universe with a small amount of spatial curvature -- negligibly impacts the lensing spectrum. We refer to this assumption as The Spatially-Flat Universe Approximation, that has been implicitly assumed in all cosmic shear studies to date. We confirm that The Spatially-Flat Universe Approximation has a negligible impact on Stage IV cosmic shear experiments.