A framework to test modified gravity using galaxy surveys

Abstract

We study the application of the marked correlation function, M, to probe gravity using the large scale structure of the Universe. We focus our efforts on testing the f(R) modified gravity theory introduced by Hu & Sawicki 2007. This model mimics the cosmic acceleration at late times through the introduction of new physics when the curvature terms are replaced by a function of the Ricci scalar R, rather than by invoking the cosmological constant. These modifications to the gravity equations lead to changes in the environments of large-scale structures that could, in principle, be used to distinguish this model from GR. We use data from the LOWZ and CMASS luminous red galaxy samples of SDSS-III BOSS to measure the marked statistic over a range of scales. To compare with the data, we create mock galaxy catalogues using the halo occupation distribution (HOD) prescription, to populate haloes from N-body simulations using GR and f(R) gravity. Using the Monte Carlo Markov Chain algorithm, we extract the number density and two-point clustering from the mock catalogues and compare with the observational measurements to constrain the HOD model parameters. Weights for individual galaxies are based on the local density information, calculated using a Voronoi tessellation, and are used to mark galaxies when computing the marked correlation function. We find that when taking into account the 1-sigma confidence interval for the best fitting HOD parameters, the marked correlation function only marginally distinguishes viable gravity models at the 1-sigma level for separations rp < 1.7 Mpc/h. As part of the process of evaluating the suitability of the N-body simulations to build mock catalogues, we address the question of the mass resolution of the halo catalogue, and introduce a simple scheme to allow the use of marginally resolved halos.