Improved BBN Constraints on the Variation of the Gravitational Constant

TL;DR

This paper refines constraints on how much the gravitational constant G could have varied during the Big Bang Nucleosynthesis epoch by using recent primordial element data, nuclear reaction rates, and CMB observations, resulting in tighter bounds than previous studies.

Contribution

It provides improved bounds on the variation of G during BBN by combining recent observational data with updated nuclear and CMB measurements, offering more stringent constraints than prior work.

Findings

G_BBN / G_0 = 0.99^{+0.06}_{-0.05} at 2σ

Linear variation rate of G: (0.7^{+3.8}_{-4.3})×10^{-12} yr^{-1}

Bounds are comparable and complementary to other astrophysical and laboratory constraints.

Abstract

Big Bang Nucleosynthesis (BBN) is very sensitive to the cosmological expansion rate. If the gravitational constant $G$ took a different value during the nucleosynthesis epoch than today, the primordial abundances of light elements would be affected. In this work, we improve the bounds on this variation using recent determinations of the primordial element abundances, updated nuclear and weak reaction rates and observations of the Cosmic Microwave Background (CMB). When combining the measured abundances and the baryon density from CMB observations by Planck, we find $G_\mathrm{BBN}/G_0 = 0.99^{+0.06}_{-0.05}$ at $2\sigma$ confidence level. If the variation of $G$ is linear in time, we find $\dot{G}/G_0 = 0.7^{+3.8}_{-4.3}\times 10^{-12} \, \mathrm{yr}^{-1}$, again at $2\sigma$. These bounds are significantly stronger than those from previous primordial nucleosynthesis studies, and are comparable and complementary to CMB, stellar, solar system, lunar laser ranging, pulsar timing and gravitational wave constraints.