Effect of Finite Nucleon Mass on Primordial Nucleosynthesis

We have modified the standard code for primordial nucleosynthesis to include the effect of finite nucleon mass on the weak-interaction rates as calculated by Seckel \cite{seckel}. We find a small, systematic increase in the $^4$He yield, $\Delta Y \simeq 0.0057\,Y$, which is insensitive to the value of the baryon-to-photon ratio $\eta$ and slightly larger than Seckel's estimate. The fractional changes in the abundances of D, $^3$He, and $^7$Li range from 0.08\% to 3\% for $10^{-11}\le \eta \le 10^{-8}$.