Varying alpha driven by the Dirac-Born-Infeld scalar field

Since about ten years ago, varying α theories attracted many attentions, mainly due to the first observational evidence from the quasar absorption spectra that the fine structure "constant" might change with cosmological time. In this Letter, we investigate the cosmic evolution of α driven by the Dirac-Born-Infeld (DBI) scalar field. To be general, we consider various couplings between the DBI scalar field and the electromagnetic field. We also confront the resulting Δ α / α with the observational constraints, and find that various cosmological evolution histories of Δ α / α are allowed. Comparing with the case of varying α driven by quintessence, the corresponding constraints on the parameters of coupling have been relaxed, thanks to the relativistic correction of the DBI scalar field.