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, $\mathrm{\Delta }Y\simeq 0.0057Y$, 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 ${10}^{-11}\le \eta \le {10}^{-8}$.