Varying alpha generalized Dirac-Born-Infeld models

We study the cosmological consequences of a class of Dirac-Born-Infeld models, and assess their viability as a candidate for the recent acceleration of the Universe. The model includes both the rolling tachyon field and the generalized Chaplygin gas models as particular limits, and phenomenologically each of these provides a possible mechanism for a deviation of the value of the dark energy equation of state from its canonical (cosmological constant) value. The field-dependent potential that is characteristic of the rolling tachyon also leads to variations of the fine-structure constant α, implying that the model can be constrained both by standard cosmological probes and by astrophysical measurements of α. Our analysis, using the latest available low-redshfit data and local constraints from atomic clock and weak equivalence principle experiments, shows that the two possible deviations of the dark energy equation of state are constrained to be log10(1+w0)V