# Geometry and growth contributions to cosmic shear observables

## TL;DR

This paper investigates how weak lensing observables are affected by the universe's expansion and structure growth, revealing cancellation effects that influence cosmological parameter constraints and highlighting the benefits of combining different effects.

## Contribution

It provides a comprehensive analysis of the interplay between geometry and growth effects on non-Gaussian weak lensing observables using simulations, extending understanding beyond analytic approaches.

## Key findings

- Cancellation between geometry and growth effects reduces sensitivity.
- Combining effects helps break parameter degeneracies.
- Errors remain similar when combining effects, with parameter correlations changing sign.

## Abstract

We explore the sensitivity of weak lensing observables to the expansion history of the universe and to the growth of cosmic structures, as well as the relative contribution of both effects to constraining cosmological parameters. We utilize ray-tracing dark-matter-only N-body simulations and validate our technique by comparing our results for the convergence power spectrum with analytic results from past studies. We then extend our analysis to non-Gaussian observables which cannot be easily treated analytically. We study the convergence (equilateral) bispectrum and two topological observables, lensing peaks and Minkowski functionals, focusing on their sensitivity to the matter density $\Omega_m$ and the dark energy equation of state $w$. We find that a cancelation between the geometry and growth effects is a common feature for all observables, and exists at the map level. It weakens the overall sensitivity by up to a factor of 3 and 1.5 for $w$ and $\Omega_m$, respectively, with the bispectrum worst affected. However, combining geometry and growth information alleviates the degeneracy between $\Omega_m$ and $w$ from either effect alone. As a result, the magnitude of marginalized errors remain similar to those obtained from growth-only effects, but with the correlation between the two parameters switching sign. These results shed light on the origin of cosmology-sensitivity of non-Gaussian statistics, and should be useful in optimizing combinations of observables.