Big Bang Nucleosynthesis in Crisis?
Abstract
A new evaluation of the constraint on the number of light neutrino species (Nnu) from big bang nucleosynthesis suggests a discrepancy between the predicted light element abundances and those inferred from observations, unless the inferred primordial 4He abundance has been underestimated by 0.014 +/- 0.004 (1 sigma) or less than 10% (95%C.L.) of 3He survives stellar processing. With the quoted systematic errors in the observed abundances and a conservative chemical evolution parameterization, the best fit to the combined data is Nnu = 2.1 +/- 0.3 (1 sigma) and the upper limit is Nnu < 2.6 (95% C.L.). The data are inconsistent with the Standard Model (Nnu = 3) at the 98.6% C.L.
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