Systematic simulations of modified gravity: chameleon models

TL;DR

This paper systematically investigates the effects of chameleon modified gravity on cosmic structure formation through extensive simulations, revealing complex phenomenology and the importance of screening mechanisms in different density regimes.

Contribution

It introduces a comprehensive simulation study of chameleon gravity models using a generic parameterization, exploring their impact on structure formation beyond linear analysis.

Findings

Chameleon screening is more efficient than other mechanisms in high-density regions.

Modified gravity effects cannot be fully captured by linear analysis at large scales.

Certain parameter regions show significant deviations from LCDM in matter power spectrum and mass function.

Abstract

In this work we systematically study the linear and nonlinear structure formation in chameleon theories of modified gravity, using a generic parameterisation which describes a large class of models using only 4 parameters. For this we have modified the N-body simulation code ECOSMOG to perform a total of 65 simulations for different models and parameter values, including the default LCDM. These simulations enable us to explore a significant portion of the parameter space. We have studied the effects of modified gravity on the matter power spectrum and mass function, and found a rich and interesting phenomenology where the difference with the LCDM paradigm cannot be reproduced by a linear analysis even on scales as large as k~0.05h/Mpc, since the latter incorrectly assumes that the modification of gravity depends only on the background matter density. Our results show that the chameleon screening mechanism is significantly more efficient than other mechanisms such as the dilaton and symmetron, especially in high-density regions and at early times, and can serve as a guidance to determine the parts of the chameleon parameter space which are cosmologically interesting and thus merit further studies in the future.