A Simple Varying-alpha Cosmology

Abstract

We investigate the cosmological consequences of a simple theory in which the electric charge $e$ is allowed to vary. The theory is locally gauge and Lorentz invariant, and satisfies general covariance. We find that in this theory the fine structure 'constant', $α$, remains almost constant in the radiation era, undergoes small increase in the matter era, but approaches a constant value when the universe starts accelerating because of the presence of a positive cosmological constant. This model satisfies geonuclear, nucleosynthesis, and CMB constraints on time-variation in $α$, while fitting simultaneously the observed accelerating universe and the recent high-redshift evidence for small $α$ variations in quasar spectra. The model also places specific restrictions on the nature of the dark matter. Further tests, involving stellar spectra and the Eötvös experiment, are proposed.