The nonlinear matter and velocity power spectra in f(R) gravity

TL;DR

This study analyzes the nonlinear matter and velocity power spectra in f(R) gravity using large N-body simulations, revealing significant deviations from LCDM predictions, especially in velocity spectra, and highlighting the importance of nonlinear effects and the chameleon mechanism.

Contribution

It provides detailed simulation-based predictions of matter and velocity power spectra in f(R) gravity, emphasizing the nonlinear regime and the limitations of linear theory for these models.

Findings

Nonlinear effects require more precise simulations than LCDM.

Velocity divergence spectra show larger deviations than matter spectra.

The evolution pattern is governed by the chameleon mechanism and model parameters.

Abstract

We study the matter and velocity divergence power spectra in a f(R) gravity theory and their time evolution measured from several large-volume N-body simulations with varying box sizes and resolution. We find that accurate prediction of the matter power spectrum in f(R) gravity places stronger requirements on the simulation than is the case with LCDM, because of the nonlinear nature of the fifth force. Linear perturbation theory is shown to be a poor approximation for the f(R) models, except when the chameleon effect is very weak. We show that the relative differences from the fiducial LCDM model are much more pronounced in the nonlinear tail of the velocity divergence power spectrum than in the matter power spectrum, which suggests that future surveys which target the collection of peculiar velocity data will open new opportunities to constrain modified gravity theories. A close investigation of the time evolution of the power spectra shows that there is a pattern in the evolution history, which can be explained by the properties of the chameleon-type fifth force in f(R) gravity. Varying the model parameter |f_R0|, which quantifies the strength of the departure from standard gravity, mainly varies the epoch marking the onset of the fifth force, as a result of which the different f(R) models are in different stages of the same evolutionary path at any given time