Effect of neutrino heating on primordial nucleosynthesis

We modify the standard code for primordial nucleosynthesis to include the effect of the slight heating of neutrinos by e^ annihilations. There is a small, systematic change in the ^4He yield, +1. 510^-4, which is insensitive to the value of the baryon-to-photon ratio for 10^-1010^-9. We also find that the baryon-to-photon ratio decreases by about 0. 5% less than the canonical factor of 411 because some of the entropy in e^ pairs is transferred to neutrinos. These results are in accord with recent analytical estimates.