Testing Einstein Gravity with Cosmic Growth and Expansion

TL;DR

This paper tests Einstein's gravity using diverse cosmological data, finding general relativity fits well and employing a Padé approximant to model deviations, ensuring accurate, unbiased combined analysis of cosmic growth and expansion.

Contribution

It introduces a method to simultaneously fit modified gravity parameters and background evolution, using a Padé approximant to accurately model deviations across time and scale.

Findings

General relativity fits combined cosmological data well.

The Padé approximant effectively captures deviations in theories like $f(R)$ and DGP.

Simultaneous fitting of growth and expansion data reduces bias and maintains accuracy.

Abstract

We test Einstein gravity using cosmological observations of both expansion and structure growth, including the latest data from supernovae (Union2.1), CMB (WMAP7), weak lensing (CFHTLS) and peculiar velocity of galaxies (WiggleZ). We fit modified gravity parameters of the generalized Poisson equations simultaneously with the effective equation of state for the background evolution, exploring the covariances and model dependence. The results show that general relativity is a good fit to the combined data. Using a Pad{\'e} approximant form for the gravity deviations accurately captures the time and scale dependence for theories like $f(R)$ and DGP gravity, and weights high and low redshift probes fairly. For current observations, cosmic growth and expansion can be fit simultaneously with little degradation in accuracy, while removing the possibility of bias from holding one aspect fixed.