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Paper: Primordial Light Element Abundances
Volume: 390, Pathways Through an Eclectic Universe
Page: 472
Authors: Molaro, P.
Abstract: After the first few minutes of its existence, the Universe evolved through conditions of temperature and density that permitted the first synthesis of astrophysically interesting abundances of D, 3He, 4He, and 7Li. Relic abundances are sensitive probes of the nucleon density, as are acoustic oscillations in the cosmic microwave background, some 400 000 years after the Big Bang; both allow a stringent cross check. The high precision estimate of the baryon density by WMAP is currently used as input parameter for standard Big Bang nucleosynthesis to interpret primordial abundances, rather than these being directly derived from the observation of light elements, as was common before. New atomic physics and the identification of systematics lead to an upward revision of the 4He primordial abundance of Yp = 0.2477±0.0029, removing a major source of tension between standard Big Bang nucleosynthesis and WMAP. The D/H ratio as measured in QSO high redshift absorbing clouds shows an excess of scatter but the mean value is found to be in spectacular agreement with the WMAP Ωb prediction. The Li/H ratio as recently redetermined in halo dwarfs is more than a factor four lower than expected. We argue that the difference reduces to a factor two when the infrared flux method Teff scale is adopted. Diffusion has been suggested to have depleted Li in halo dwarfs by the required amount to remove the gap; however, this would imply an implausibly high abundance of the more fragile 6Li detected in some halo dwarfs, thus leaving the puzzle open.
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