Structure Formation in Modified Gravity Scenarios

TL;DR

This paper investigates how modified gravity models affect structure formation in the universe, analyzing linear to nonlinear scales to improve theoretical predictions for observational tests.

Contribution

It introduces a combined perturbative and resummation approach to accurately model structure growth in modified gravity scenarios, extending beyond low-order results.

Findings

Standard perturbation theory is insufficient for accurate predictions.

Resummation techniques improve modeling of the power spectrum.

Modified gravity effects are most detectable on weakly nonlinear scales.

Abstract

We study the growth of structures in modified gravity models where the Poisson equation and the relationship between the two Newtonian potentials are modified by explicit functions of space and time. This parameterisation applies to the $f(R)$ models and more generally to screened modified gravity models. We investigate the linear and weakly nonlinear regimes using the "standard" perturbative approach and a resummation technique, while we use the spherical dynamics to go beyond low-order results. This allows us to estimate the matter density power spectrum and bispectrum from linear to highly nonlinear scales, the full probability distribution of the density contrast on weakly nonlinear scales, and the halo mass function. We analyse the impact of modifications of gravity on these quantities for a few realistic models. In particular, we find that the standard one-loop perturbative approach is not sufficiently accurate to probe these effects on the power spectrum and it is necessary to use resummation methods even on weakly nonlinear scales which provide the best observational window for modified gravity as relative deviations from General Relativity do not grow significantly on smaller scales where theoretical predictions become increasingly difficult.