Cosmological and astrophysical constraints on tachyon dark energy models

TL;DR

This paper uses recent cosmological and astrophysical data to tightly constrain tachyon dark energy models, showing they behave almost like a cosmological constant due to extremely slow field dynamics.

Contribution

It provides the most stringent constraints to date on tachyon dark energy models by combining supernova and fine-structure constant measurements.

Findings

Constraints imply the dark energy equation of state is very close to -1.

Current data cannot distinguish these models from a cosmological constant.

Detection of alpha variations could differentiate these models in the future.

Abstract

Rolling tachyon field models are among the candidates suggested as explanations for the recent acceleration of the Universe. In these models the field is expected to interact with gauge fields and lead to variations of the fine-structure constant $\alpha$. Here we take advantage of recent observational progress and use a combination of background cosmological observations of Type Ia supernovas and astrophysical and local measurements of $\alpha$ to improve constraints on this class of models. We show that the constraints on $\alpha$ imply that the field dynamics must be extremely slow, leading to a constraint of the present-day dark energy equation of state $(1+w_0)<2.4\times10^{-7}$ at the $99.7\%$ confidence level. Therefore current and forthcoming standard background cosmology observational probes can't distinguish this class of models from a cosmological constant, while detections of $\alpha$ variations could possibly do so since they would have a characteristic redshift dependence.