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

Higher-dimensional theories have the remarkable feature of predicting a time (and hence redshift) dependence of the ``fundamental'' four dimensional constants on cosmological time scales. In this paper, we update the bounds on a possible variation of the fine structure constant α at the time of big bang nucleosynthesis (z~10¹⁰) and cosmic microwave background (CMB) (z~10³). Using the recently released high-resolution CMB anisotropy data and the latest estimates of primordial abundances of ⁴He and D, we do not find evidence for a varying {α} at more than a one-sigma level at either epoch.