The electromagnetic coupling and the dark side of the Universe

We examine the properties of dark energy and dark matter through the study of the variation of the electromagnetic coupling. For concreteness, we consider the unification model of dark energy and dark matter, the generalized Chaplygin gas model (GCG), characterized by the equation of state $p=-\frac{A}{\rho^\alpha}$, where $p$ is the pressure, $\rho$ is the energy density and $A$ and $\alpha$ are positive constants. The coupling of electromagnetism with the GCG's scalar field can give rise to such a variation. We compare our results with experimental data, and find that the degeneracy on parameters $\alpha$ and $A_s$, $A_s \equiv A / \rho_{ch0}^{1+\alpha}$, is considerable.