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, ΔY congruent+1.5x10-4, which is insensitive to the value of the baryon-to-photon ratio η for 10-10 approx-lt η approx-lt 10-9. We also find that the baryon-to-photon ratio decreases by about 0.5% less than the canonical factor of 4/11 because some of the entropy in e± pairs is transferred to neutrinos. These results are in accord with recent analytical estimates