Revised primordial helium abundance based on new atomic data

We have derived a primordial helium abundance of Y-p = 0.2477 +/- 0: 0029, based on new atomic physics computations of the recombination coefficients of He I and of the collisional excitation of the H I Balmer lines together with observations and photoionization models of metal-poor extragalactic H II regions. The new atomic data increase our previous determination of Y-p by 0.0086, a very significant amount. By combining our Y-p result with the predictions made by the standard big bang nucleosynthesis model, we find a baryon-to-photon ratio, eta, in excellent agreement both with the eta-value derived by the primordial deuterium abundance value observed in damped Ly alpha systems and with the one obtained from the WMAP observations.