Testing modified gravity scenarios with direct peculiar velocities

TL;DR

This paper explores how galaxy clustering and peculiar velocity measurements can distinguish modified gravity theories from General Relativity, providing forecasts for future surveys to constrain deviations.

Contribution

It demonstrates that galaxy and velocity correlation functions can effectively differentiate between GR and modified gravity models like DGP and f(R), with specific forecasted constraints.

Findings

Correlation functions can distinguish gravity models.

Forecasted constraints on f(R) and DGP parameters.

Velocity surveys can test gravity modifications at z=0.5.

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 $\Lambda$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 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 $20\%$ distance accuracy would constrain model parameters to 3-$\sigma$ confidence limits $\log_{10}|f_{R0}| < -6.45$ for $f(R)$ gravity and $r_c > 2.88 \, c/H_0$ for nDGP, assuming a fiducial GR model.