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

Abstract

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 $\ensuremath{\alpha}$ at the time of big bang nucleosynthesis $(z\ensuremath{\sim}{10}^{10})$ and cosmic microwave background (CMB) $(z\ensuremath{\sim}{10}^{3}).$ 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 \ensuremath{\alpha} at more than a one-sigma level at either epoch.