Disformal Scalar Fields and the Dark Sector of the Universe

TL;DR

This paper explores how disformal transformations applied to scalar fields can model the dark sector, unifying various dark energy models and comparing their predictions with cosmological data.

Contribution

It introduces a disformal scalar field framework that encompasses multiple dark energy models and performs a comprehensive comparison with observational data.

Findings

Disformal scalar fields can replicate many dark energy models.

Certain parameter ranges are consistent with cosmological observations.

Models with excessive early dark energy or slow acceleration transitions are ruled out.

Abstract

Disformal transformations have proven to be very useful to devise models of the dark sector. In the present paper we apply such transformation to a single scalar field theory as a way to drive the field into a slow roll phase. The canonical scalar field Lagrangian, when coupled to a disformal metric, turns out to have relations to bimetric dark matter theories and to describe many specific dark energy models at various limits, thus providing a surprisingly simple parametrisation of a wide variety of models including tachyon, Chaplygin gas, K-essence and dilatonic ghost condensate. We investigate the evolution of the background and linear perturbations in disformal quintessence in order to perform a full comparison of the predictions with the cosmological data. The dynamics of the expansion, in particular the mechanism of the transition to accelerating phase, is described in detail. We then study the effects of disformal quintessence on cosmic microwave background (CMB) anisotropies and large scale structures (LSS). A likelihood analysis using the latest data on wide-ranging SNIa, CMB and LSS observations is performed allowing variations in six cosmological parameters and the two parameters specifying the model. We find that while a large region of parameter space remains compatible with observations, models featuring either too much early dark energy or too slow transition to acceleration are ruled out.