New limits on the variability of G from big bang nucleosynthesis

We revise limits on the value of G during primordial nucleosynthesis by incorporating new measurements of the neutron half-life along with the most recent reaction rate uncertainties. In doing this we follow D, ³He, and ⁷Li as G varies to determine how this variation affects limits on the baryon-to-photon ratio (μ). We then incorporate these new limits into the ⁴He predictions to limit G as a function of the number of relativistic species at the time of nucleosynthesis. If the number of such species (≥2) is not greater than the upper limit on the number of light neutrinos measured at CERN and the primordial abundance of ⁴He was between (22-25)%, then 1.4>G_nucl G_today>0.7. If G(t) ≈ t^-α, this would translate into a limit 0.008>α>-0.009, or an approximate limit ( G G)_today<±9×10^-13yr^-1.