Zusammenfassung
We report the discovery and analysis of the most metal-poor damped
Lyman-alpha (DLA) system currently known, which also displays the Lyman series
absorption lines of neutral deuterium. The average O/H abundance of this
system is O/H = -2.804 +/- 0.015, which includes an absorption component with
O/H = -3.07 +/- 0.03. Despite the unfortunate blending of many weak D I
absorption lines, we report a precise measurement of the deuterium abundance of
this system. Using the six highest quality and self-consistently analyzed
measures of D/H in DLAs, we report tentative evidence for a subtle decrease of
D/H with increasing metallicity. This trend must be confirmed with future high
precision D/H measurements spanning a range of metallicity. A weighted mean of
these six independent measures provides our best estimate of the primordial
abundance of deuterium, 10^5 (D/H)_P = 2.547 +/- 0.033 (log_10 (D/H)_P =
-4.5940 +/- 0.0056). We perform a series of detailed Monte Carlo calculations
of Big Bang nucleosynthesis (BBN) that incorporate the latest determinations of
several key nuclear cross sections, and propagate their associated uncertainty.
Combining our measurement of (D/H)_P with these BBN calculations yields an
estimate of the cosmic baryon density, 100 Omega_B,0 h^2(BBN) = 2.156 +/-
0.020, if we adopt the most recent theoretical determination of the
d(p,gamma)3He reaction rate. This measure of Omega_B,0 h^2 differs by ~2.3
sigma from the Standard Model value estimated from the Planck observations of
the cosmic microwave background. Using instead a d(p,gamma)3He reaction rate
that is based on the best available experimental cross section data, we
estimate 100 Omega_B,0 h^2(BBN) = 2.260 +/- 0.034, which is in somewhat better
agreement with the Planck value. Forthcoming measurements of the crucial
d(p,gamma)3He cross section may shed further light on this discrepancy.
Nutzer