Precision rates for nucleon weak interactions in primordial nucleosynthesis and 4He abundance

We report the results of a detailed calculation of nucleon weak interactions relevant for the neutron to proton density ratio at the onset of primordial nucleosynthesis. Radiative electromagnetic corrections, finite nucleon mass terms, thermal radiative effects on weak processes and on neutrino temperature are taken into account to reduce the theoretical uncertainty on n <-> p rates to 1%. This translates into a sensitivity in the He-4 mass fraction Y-p prediction up to 10(-4). We find a positive total correction to the Born prediction delta Y-p similar or equal to 0.004. (C) 1999 Elsevier Science B.V.