# Cosmological constraints on scalar-tensor gravity and the variation of the gravitational constant

## TL;DR

This paper uses Planck 2015 CMB and BAO data to place tight constraints on the variation of the gravitational constant over cosmic time within scalar-tensor gravity theories.

## Contribution

It provides the first combined analysis of CMB and BAO data to constrain the time variation of G in scalar-tensor theories, improving previous bounds.

## Key findings

- Time variation of G constrained to less than 0.2% at 95% CL
- BAO data improves constraints by over 10%
- Constraints depend on prior choices

## Abstract

We present cosmological constraints on the scalar-tensor theory of gravity by analyzing the angular power spectrum data of the cosmic microwave background obtained from the Planck 2015 results together with the baryon acoustic oscillations (BAO) data. We find that the inclusion of the BAO data improves the constraints on the time variation of the effective gravitational constant by more than $10\%$, that is, the time variation of the effective gravitational constant between the recombination and the present epochs is constrained as $G_{\rm rec}/G_0-1 <1.9\times 10^{-3}\ (95.45\%\ {\rm C.L.})$ and $G_{\rm rec}/G_0-1 <5.5\times 10^{-3}\ (99.99 \%\ {\rm C.L.})$. We also discuss the dependence of the constraints on the choice of the prior.