Tension of the $E_G$ statistic and RSD data with Planck/$\Lambda$CDM and implications for weakening gravity

TL;DR

This paper combines recent $E_G$ and RSD data to test deviations from General Relativity, finding increased tension with the Planck/$ m f extLambda$CDM model, suggesting possible weakening of gravity at low redshifts.

Contribution

It provides an updated compilation of $E_G$ data and analyzes its tension with RSD data against the standard model, highlighting potential signs of modified gravity.

Findings

Tension increases from 3.5σ to 6σ when including $E_G$ data.

Results suggest weaker effective Newton constants at low redshifts.

Supports previous hints of modified gravity weakening.

Abstract

The $E_G$ statistic is a powerful probe for detecting deviations from GR by combining weak lensing (WL), real-space clustering and redshift space distortion (RSD) measurements thus probing both the lensing and the growth effective Newton constants ($G_L$ and $G_{eff}$). We construct an up to date compilation of $E_G$ statistic data including both redshift and scale dependence ($E_G(R,z)$). We combine this $E_G$ data compilation with an up to date compilation of $f\sigma_8$ data from RSD observations to identify the current level of tension between the Planck/$\Lambda$CDM standard model based on general relativity and a general model independent redshift evolution parametrization of $G_L$ and $G_{eff}$. Each $f\sigma_8$ datapoint considered has been published separately in the context of independent analyses of distinct galaxy samples. However, there are correlations among the datapoints considered due to overlap of the analyzed galaxy samples. Due to these correlations the derived levels of tension of the best fit parameters with Planck/$\Lambda$CDM are somewhat overestimated but this is the price to pay for maximizing the information encoded in the compilation considered. We find that the level of tension increases from about $3.5\sigma$ for the $f\sigma_8$ data compilation alone to about $6\sigma$ when the $E_G$ data are also included in the analysis. The direction of the tension is the same as implied by the $f\sigma_8$ RSD growth data alone (lower $\Omega_m$ and/or weaker effective Newton constant at low redshifts for both the lensing and the growth effective Newton constants ($G_L$ and $G_{eff}$)). These results further amplify the hints for weakening modified gravity discussed in other recent analyses.