Tachyonic vs Quintessence dark energy: linear perturbations and CMB data

TL;DR

This study compares quintessence and tachyonic dark energy models using linear perturbation theory and CMB data, showing they are nearly indistinguishable in the linear regime and that current observations weakly constrain their parameters.

Contribution

It demonstrates the difficulty in distinguishing between quintessence and tachyonic dark energy models with linear perturbations and existing CMB data, especially for models with $(1 + w) \, \ll 1$.

Findings

Models are hard to distinguish in the linear regime.

Current CMB data weakly constrain potential parameters.

Intrinsic parameters remain weakly constrained by Planck data.

Abstract

We use linear perturbation theory to study perturbations in dynamical dark energy models. We compare quintessence and tachyonic dark energy models with identical background evolution. We write the corresponding equations for different models in a form that makes it easier to see that the two models are very hard to distinguish in the linear regime, especially for models with $(1 + w) \ll 1$. We use Cosmic Microwave Background data and parametric representations for the two models to illustrate that they cannot be distinguished for the same background evolution with existing observations. Further, we constrain tachyonic models with the Planck data. We do this analysis for exponential and inverse square potentials and find that the intrinsic parameters of the potentials remain very weakly constrained. In particular, this is true in the regime allowed by low redshift observations.