Testing modified gravity scenarios with direct peculiar velocities

Abstract

The theoretical basis of dark energy remains unknown and could signify a need to modify the laws of gravity on cosmological scales. In this study, we investigate how the clustering and motions of galaxies can be used as probes of modified gravity theories, using galaxy and direct peculiar velocity auto- and cross-correlation functions. We measure and fit these correlation functions in simulations of ∧CDM, DGP, and f(R) cosmologies and, by extracting the characteristic parameters of each model, we show that these theories can be distinguished from General Relativity (GR) using these measurements. We present forecasts showing that with sufficiently large data samples, this analysis technique is a competitive probe that can help place limits on allowed deviations from GR. For example, a peculiar velocity survey reaching to z = 0.5 with 20 per cent distance accuracy would constrain model parameters to 3-σ confidence limits log10|fR0| < −6.45 for f(R) gravity and rc > 2.88 c/H0 for nDGP, assuming a fiducial GR model.