Stage-IV Cosmic Shear with Modified Gravity and Model-independent Screening

TL;DR

This paper forecasts constraints on modified gravity theories using Stage-IV cosmic shear data, emphasizing the importance of screening effects and their degeneracy with baryonic feedback for accurate cosmological parameter estimation.

Contribution

It introduces a power spectrum emulator and a halo-model based screening approach, demonstrating their effectiveness in analyzing modified gravity with cosmic shear data.

Findings

Screening transition is degenerate with baryonic feedback.

Neglecting screening causes biased cosmological parameters.

Forecasted uncertainties on the growth index are around 10%.

Abstract

We forecast constraints on minimal model-independent parametrisations of several Modified Gravity theories using mock Stage-IV cosmic shear data. We include nonlinear effects and screening, which ensures recovery of General Relativity on small scales. We introduce a power spectrum emulator to accelerate our analysis and evaluate the robustness of the growth index parametrisation with respect to two cosmologies: $\Lambda$CDM and the normal branch of the DGP model. We forecast the uncertainties on the growth index $\gamma$ to be of the order $\sim 10\%$. We find that our halo-model based screening approach demonstrates excellent performance, meeting the precision requirements of Stage-IV surveys. However, neglecting the screening transition results in biased predictions for cosmological parameters. We find that the screening transition shows significant degeneracy with baryonic feedback, requiring a much better understanding of baryonic physics for its detection. Massive neutrinos effects are less prominent and challenging to detect solely with cosmic shear data.