Recent Deuterium Observations and Big Bang Nucleosynthesis: A New Paradigm?

Abstract

A new observation of D in a primordial gas cloud, made using the high resolution spectrograph at the Keck telescope, indicates an abundance $D/H=(1.9-2.5)\times 10^{-4}$ \cite{SCHR}. Since deuterium is destroyed by stars, and the predicted Big Bang Nucleosynthesis (BBN) abundance falls monotonically with increasing baryon density, deuterium places a reliable upper limit on the baryon density of the universe. Because the new measurement is substationally larger than previous, galactic estimates, it would force a reassessment of BBN predictions--- if it is confirmed. Using a new BBN Monte Carlo code and analysis technique \cite{KK} we derive constraints implied by a lower limit of $D/H=1.9\times 10^{-4}$. We find ${\Omega }_B\le .0068h^{-2}$, which is definitively incompatible with baryonic halo dark matter. We also explore implications of combining the D measurement with other light element abundances. ${}^{7}Li$ provides a lower bound, ${\Omega }_B\ge .004h^{-2}$. Also, the initial ${}^{4}He$ mass fraction ($Y_p$) would have to be less than $23.5\%$, assuming 3 light neutrino species---in good agreement with present best fits. Finally, observational upper limits of $Y_p\le 24\%$ and ${}^{7}Li/H\le 2.3\times 10^{-10}$ would allow the number of neutrinos to be as big as 3.9.

10 pages, latex, 2 uuencoded figures appended, one ps file available by anonymous ftp (ftp.cwru.edu, physics/bbndeut/Bbnfig1.ps.Z) CWRU-P6-94

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