Nonlinear growth in modified gravity theories of dark energy

TL;DR

This paper investigates the nonlinear growth of cosmic structures in modified gravity theories of dark energy through N-body simulations, assessing the accuracy of existing analytical models in predicting these effects.

Contribution

It provides the first comprehensive comparison of analytical nonlinear matter power spectrum fits with N-body simulations in various modified gravity models.

Findings

Analytical fits match simulation results within 1σ across models.

No significant difference found between the analytical models tested.

Simulations cover a wide redshift range from z=50 to today.

Abstract

Theoretical differences in the growth of structure offer the possibility that we might distinguish between modified gravity theories of dark energy and \LambdaCDM. A significant impediment to applying current and prospective large scale galaxy and weak lensing surveys to this problem is that, while the mildly nonlinear regime is important, there is a lack of numerical simulations of nonlinear growth in modified gravity theories. A major question exists as to whether existing analytical fits, created using simulations of standard gravity, can be confidently applied. In this paper we address this, presenting results of N-body simulations of a variety of models where gravity is altered including the Dvali, Gabadadze and Porrati model. We consider modifications that alter the Poisson equation and also consider the presence of anisotropic shear stress that alters how particles respond to the gravitational potential gradient. We establish how well analytical fits of the matter power spectrum by Peacock and Dodds and Smith et al. are able to predict the nonlinear growth found in the simulations from z=50 up to today, and also consider implications for the weak lensing convergence power spectrum. We find that the analytical fits provide good agreement with the simulations, being within 1\sigma of the simulation results for cases with and without anisotropic stress and for scale-dependent and independent modifications of the Poisson equation. No strong preference for either analytical fit is found.