Varying Alpha Generalized Dirac-Born-Infeld Models

TL;DR

This paper investigates Dirac-Born-Infeld cosmological models with varying alpha, constraining their parameters using observational data, and finds that the potential must be extremely flat for viability.

Contribution

It introduces a generalized class of DBI models including tachyon and Chaplygin gas limits, analyzing their cosmological and fine-structure constant variations.

Findings

Dark energy equation of state deviations are tightly constrained.

Potential slope must be very flat, with $oxed{ ext{log}_{10} ext{(} ext{potential slope} ext{)} < -5.36}$.

Models are consistent with current low-redshift and astrophysical data.

Abstract

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 $\alpha$, implying that the model can be constrained both by standard cosmological probes and by astrophysical measurements of $\alpha$. 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 $\log_{10}{(1+w_0)_V}<-7.85$ and $\log_{10}{(1+w_0)_C}<-0.85$, respectively for the rolling tachyon and Chaplygin components, both being at the $95.4\%$ confidence level (although the latter depends on the choice of priors, in a way that we quantify). Alternatively, the $95.4\%$ confidence level bound on the dimensionless slope of the potential is $\log_{10}{\lambda}<-5.36$. This confirms previous analyses indicating that in these models the potential needs to be extremely flat.