Three-Point Correlations in f(R) Models of Gravity

TL;DR

This paper investigates three-point correlations in f(R) gravity models, finding that deviations from standard gravity are small and can be approximated using linear growth factors, simplifying predictions for large-scale structure.

Contribution

It demonstrates that three-point correlations in f(R) gravity models are nearly universal and can be predicted with linear growth factors, simplifying analysis of such models.

Findings

Deviations in the bispectrum depend on time, scale, and shape.

Reduced bispectrum Q deviations are at the percent level.

Weakly nonlinear clustering is not fundamentally altered in these models.

Abstract

Modifications of general relativity provide an alternative explanation to dark energy for the observed acceleration of the universe. We calculate quasilinear effects in the growth of structure in f(R) models of gravity using perturbation theory. We find significant deviations in the bispectrum that depend on cosmic time, length scale and triangle shape. However the deviations in the reduced bispectrum Q for f(R) models are at the percent level, much smaller than the deviations in the bispectrum itself. This implies that three-point correlations can be predicted to a good approximation simply by using the modified linear growth factor in the standard gravity formalism. Our results suggest that gravitational clustering in the weakly nonlinear regime is not fundamentally altered, at least for a class of gravity theories that are well described in the Newtonian regime by the parameters G_eff and Phi/Psi. This approximate universality was also seen in the N-body simulation measurements of the power spectrum by Stabenau and Jain (2006), and in other recent studies based on simulations. Thus predictions for such modified gravity models in the regime relevant to large-scale structure observations may be less daunting than expected on first principles. We discuss the caveats that apply to such predictions.