Early-universe constraints on a time-varying fine structure constant

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  • 8 February 2001
Abstract
Recent high-resolution CMB anisotropy data seem to point to a value for the baryon density larger than what is predicted by Standard Big Bang Nucleosynthesis, ruling out a large set of standard cosmological models. However, present CMB data can be made compatible with a lower value for the baryon density if the fine-structure constant alpha was smaller in the past. In this letter we produce early-universe constraints on a time-varying alpha by a joint analysis of the latest CMB and BBN data. We find strong constraints on the variation of alpha from BBN, Delta alpha/alpha=(-7 \pm 9)10^-3 (95% C.L.), marginally compatible with the CMB result, Delta alpha/alpha=-0.10 \pm 0.05 (68 % C.L.). We conclude that the varying alpha scenario may still solve the CMB-BBN discrepancy, but that may require a non-monotonic red-shift behaviour for the fine structure constant

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