Primordial Nucleosynthesis : Accurate Predictions

Big Bang Nucleosynthesis (BBN) represents a key subject of modern cosmology since it is a powerful tool to study fundamental interactions. In the recent years, the improvement on the measurement accuracy of light primordial nu-clei abundances allowed BBN to enter in a sort of precision era. In view of this, a great theoretical effort has been devoted to make theoretical predictions comparably accurate. Unfortunately, as far as D, 3 He and 7 Li are concerned, the theoretical uncertainty on their primordial abundances is greatly dominated by a poor knowledge of many nuclear reactions involved in their production. On the contrary, the 4 He abundance results into a robust prediction and thus an effort to reduce at less than 1% its theoretical uncertainty is meaningful. To improve the accuracy on the prediction of 4 He abundance in Ref. [1] we performed a thoroughly analysis of all corrections to the pro-ton/neutron conversion rates, ν e + n ↔ e − + p, e + + n ↔ ν e + p, n ↔ e − + ν e + p which fix at the freeze out temperature ∼ 1 M eV the neutron to proton density ratio. The Born rates, obtained in the tree level V −A limit and with infinite nucleon mass, have been corrected to take into account three classes of relevant effects: electromagnetic radiative corrections, finite nucleon mass corrections and plasma effects.