N-body Simulations for f(R) Gravity using a Self-adaptive Particle-Mesh Code

Gong-Bo Zhao, Baojiu Li, Kazuya Koyama (LaSMoG Consortium)

We perform high resolution N-body simulations for f(R) gravity based on a self-adaptive particle-mesh code MLAPM. The Chameleon mechanism that recovers General Relativity on small scales is fully taken into account by self-consistently solving the non-linear equation for the scalar field. We independently confirm the previous simulation results, including the matter power spectrum, halo mass function and density profiles, obtained by Oyaizu et al. (Phys.Rev.D 78, 123524, 2008) and Schmidt et al. (Phys.Rev.D 79, 083518, 2009), and extend the resolution up to k~20 h/Mpc for the measurement of the matter power spectrum. Based on our simulation results, we discuss how the Chameleon mechanism affects the clustering of dark matter and halos on full non-linear scales.

Project Introduction

The acceleration of the Universe remains an enigma. To understand this acceleration, people have to introduce a weird component, called Dark Energy, in the framework of General Relativity (GR). However, GR needs to be tested on cosmic scales. Previous studies show that the cosmic acceleration could be realised by modification of GR on cosmological scales without introducing dark energy. If GR gets modified, the structure formation will be very different from that in GR, although the expansion history remains the same as in a LCDM universe. Therefore the observation of the large scale structure of the universe could in principle provide new test of GR on cosmic scales, yet this kind of test cannot be done without the help of simulations since the structure formation process is highly nonlinear.

The aim of the project is to perform large simulations for modified gravity models including f(R), DGP, etc. We formed the Large Simulation for Modified Gravity (LasMoG) consortium in November 2009. The current members are Baojiu Li (Cambridge), Kazuya Koyama (ICG) and myself. We have finished the f(R) simulation using a modified self-adaptive particle-mesh code MLAPM. We have got much better resolution for matter power spectrum than the previous works using only 256^3 particles. We have transplanted our code to Ramses to run much larger simulations to investigate more physics in modified gravity models including the symmetron, dilaton, general chameleon, DGP, and Galileon models.

f(R) Simulation Gallery