Galaxy Cluster Statistics in Modified Gravity Cosmologies

Modification of gravity (MG) on cosmological scales is one possible explanation for the accelerated expansion of the universe. Here we investigate the statistics of the distribution of galaxy cluster-sized haloes as a probe of gravity. We analyze the output of the ELEPHANT simulations, which evolved 1024^3 particles in a 1024 Mpc/h box from identical initial conditions using both DGP and f(R) gravity with various parameters. From each simulation we extract the cluster mass function (CMF), power spectrum (PS), and mean pairwise velocity (MPV) at several redshifts. MPV shows the greatest promise of constraining MG theories as we observed fractional differences between MG theories and GR ranging from 0.04% to 45% for the models considered. Upcoming microwave background experiments, including Simons Observatory and CMB-S4, will detect tens of thousands of galaxy clusters, which will provide substantial probes of modified gravity using these statistics.