A New Nucleosynthesis Constraint on the Variation of G

TL;DR

Big bang nucleosynthesis can provide constraints on the expansion rate at that time, limits on possible variations in Newton's constant, G, and recent measurements of the primordial deuterium abundance in quasar absorption systems now allows a new tighter constraint on G to be derived without recourse to considerations of helium or lithium abundances.

Abstract

Big Bang Nucleosynthesis can provide, via constraints on the expansion rate at that time, limits on possible variations in Newton's Constant, $G$. The original analyses were performed before an independent measurement of the baryon-to-photon ratio from the cosmic microwave background was available. Combining this with recent measurements of the primordial deuterium abundance in quasar absorption systems now allows one to derive a new tighter constraint on $G$ without recourse to considerations of helium or lithium abundances. We find that, compared to todays value, $G_0$, $G_{BBN}/G_0=1.01^{+0.20}_{-0.16}$ at the 68.3% confidence level. If we assume a monotonic power law time dependence, $G\propto t^{-α}$, then the constraint on the index is $-0.004 < α< 0.005$. This would translate into $-3\times10^{-13} \textrm{yr}^{-1} < (\dot G/G)_{\textrm{today}} < 4 \times 10^{-13} \textrm{yr}^{-1}$.

Figures (1)

• Figure 1: Observational limits and theoretical expections for $D/H$ versus $\eta$. The one (light shading) and 2 (dark shading) sigma observational uncertainties for $D/H$ and $\eta$ are shown. They do not appear as ellipses due to the linear scale in $D/H$ but logarithmic uncertainties from the observations. The BBN predictions are shown as the solid curves where the width is the $3\%$ theoretical uncertainties. Three different values of $G_{BBN}/G_0$ are shown.