New Nucleosynthesis Constraint on the Variation of G

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 today’s value, G₀, G_BBN/G₀=1.01_-0.16^+0.20 at the 68% confidence level.