Probing the Cosmological Principle with weak lensing shear

TL;DR

This paper explores how weak gravitational lensing shear measurements can test the Cosmological Principle by detecting anisotropic expansion, proposing a method to constrain anisotropy using large-scale shear mode correlations.

Contribution

It demonstrates that large-scale shear $E$-$B$ mode cross-correlations can serve as a probe for late-time anisotropic expansion, providing a new observational test of the Cosmological Principle.

Findings

Large-scale shear $E$-$B$ correlations can indicate anisotropic expansion.

Euclid-like surveys could detect signals of late-time anisotropy.

The method constrains the magnitude and possibly the direction of anisotropic expansion.

Abstract

The Cosmological Principle is a cornerstone of the standard model of cosmology and shapes how we view the Universe and our place within it. It is imperative, then, to devise multiple observational tests which can identify and quantify possible violations of this foundational principle. One possible method of probing large-scale anisotropies involves the use of weak gravitational lensing. We revisit this approach in order to analyse the imprint of late-time anisotropic expansion on cosmic shear. We show that the cross-correlation of shear $E$- and $B$-modes on large scales can be used to constrain the magnitude (and possibly direction) of anisotropic expansion. We estimate the signal to noise for multipoles $10\lesssim \ell\lesssim 100$ that is achievable by a Euclid-like survey. Our findings suggest that such a survey could detect the $E$-$B$ signal for reasonable values of the late-time anisotropy parameter.