PRECISION MEASURES OF THE PRIMORDIAL ABUNDANCE OF DEUTERIUM

We report the discovery of deuterium absorption in the very metal-poor ([Fe/H] = -2.88) damped Ly alpha system at z(abs) = 3.06726 toward the QSO SDSS J1358+6522. On the basis of 13 resolved D I absorption lines and the damping wings of the Hi Ly alpha transition, we have obtained a new, precise measure of the primordial abundance of deuterium. Furthermore, to bolster the present statistics of precision D/H measures, we have reanalyzed all of the known deuterium absorption-line systems that satisfy a set of strict criteria. We have adopted a blind analysis strategy (to remove human bias) and developed a software package that is specifically designed for precision D/H abundance measurements. For this reanalyzed sample of systems, we obtain a weighted mean of (D/H)(p) = (2.53 +/- 0.04) x 10(-5), corresponding to a universal baryon density 100 Omega(b,0) h(2) = 2.202 +/- 0.046 for the standard model of big bang nucleosynthesis (BBN). By combining our measure of (D/H)(p) with observations of the cosmic microwave background (CMB), we derive the effective number of light fermion species, N-eff = 3.28 +/- 0.28. We therefore rule out the existence of an additional (sterile) neutrino (i.e., N-eff = 4.046) at 99.3% confidence (2.7 sigma), provided that the values of N-eff and of the baryon-to-photon ratio (eta(10)) did not change between BBN and recombination. We also place a strong bound on the neutrino degeneracy parameter, independent of the He-4 primordial mass fraction, Y-P:xi(D) = + 0.05 +/- 0.13 based only on the CMB+(D/H)(p) observations. Combining this value of xi(D) with the current best literature measure of Y-P, we find a 2 sigma upper bound on the neutrino degeneracy parameter, vertical bar xi vertical bar <= +0.062.