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 $\alpha$ at the time of big bang nucleosynthesis $\left(z\sim {10}^{10}\right)$ and cosmic microwave background (CMB) $\left(z\sim {10}^3\right).\mathrm{}$ Using the recently released high-resolution CMB anisotropy data and the latest estimates of primordial abundances of ${}^4\mathrm{He}$ and D, we do not find evidence for a varying α at more than a one-sigma level at either epoch.