Measuring $α$ in the Early Universe: CMB Temperature, Large-Scale Structure and Fisher Matrix Analysis

Abstract

We extend our recent work on the effects of a time-varying fine-structure constant $α$ in the cosmic microwave background, by providing a thorough analysis of the degeneracies between $α$ and the other cosmological parameters, and discussing ways to break these with both existing and/or forthcoming data. In particular, we present the state-of-the-art CMB constraints on $α$, through a combined analysis of the BOOMERanG, MAXIMA and DASI datasets. We also present a novel discussion of the constraints on $α$ coming from large-scale structure observations, focusing in particular on the power spectrum from the 2dF survey. Our results are consistent with no variation in $α$ from the epoch of recombination to the present day, and restrict any such (relative) variation to be less than about 4%. We show that the forthcoming MAP and (particularly) Planck experiments will be able to break most of the currently existing degeneracies between $α$ and other parameters, and measure $α$ to better than percent accuracy.