Early-universe constraints on a time-varying fine structure constant - art. no. 103505

Higher-dimensional theories have the remarkable feature of predicting a tim e (and hence redshift) dependence of the "fundamental" four dimensional con stants on cosmological time scales. In this paper, we update the bounds on a possible variation of the fine structure constant a at the time of big ba ng nucleosynthesis (z similar to 10(10)) and cosmic microwave background (C MB) (z similar to 10(3)). Using the recently released high-resolution CMB a nisotropy data and the, latest estimates of primordial abundances of He-4 a nd D, we do not find evidence for a varying alpha at more than a one sigma level at either epoch.