Assessing theoretical uncertainties for cosmological constraints from weak lensing surveys

Abstract

Weak gravitational lensing is a powerful probe which is used to constrain the standard cosmological model and its extensions. With the enhanced statistical precision of current and upcoming surveys, high-accuracy predictions for weak lensing statistics are needed to limit the impact of theoretical uncertainties on cosmological parameter constraints. For this purpose, we present a comparison of the theoretical predictions for the nonlinear matter and weak lensing power spectra, based on the widely used fitting functions (mead and rev-halofit), emulators (EuclidEmulator, EuclidEmulator2, BaccoEmulator and CosmicEmulator) and N-body simulations (Pkdgrav3). We consider the forecasted constraints on the Λ CDM and wCDM models from weak lensing for stage III and stage IV surveys. We study the relative bias on the constraints and their dependence on the assumed prescriptions. Assuming a wCDM cosmology, we find that the relative agreement on the S8 parameter is between 0.2 − 0.3σ for a stage III-like survey between the above predictors. For a stage IV-like survey the agreement becomes 1.4 − 3.0σ. In the $\texttt {wCDM}$ scenario, we find broader S8 constraints, and agreements of 0.18 − 0.26σ and 0.7 − 1.7σ for stage III and stage IV surveys, respectively. The accuracies of the above predictors therefore appear adequate for stage III surveys, while the fitting functions would need improvements for future stage IV surveys. Furthermore, we find that, of the fitting functions, $\texttt {mead}$ provides the best agreement with the emulators. We discuss the implication of these findings for the preparation of future weak lensing surveys, and the relative impact of theoretical uncertainties to other systematics.