Disformally Coupled Quintessence

TL;DR

This paper explores a generalized disformal coupling in scalar field dark energy models, revealing new fixed points and cosmological behaviors, with implications for early universe dynamics and late-time acceleration.

Contribution

It introduces a broader class of disformal transformations depending on the scalar field and its derivatives, expanding the phenomenology of coupled quintessence models.

Findings

New disformal fixed points with unique cosmological features

Broader stability regions for coupled scalar field models

Suppressed late-time disformal effects in viable cosmologies

Abstract

In this work we consider a cosmological model in which dark energy is portrayed by a canonical scalar field which is allowed to couple to the other species by means of a disformal transformation of the metric. We revisit the current literature by assuming that the disformal function in the metric transformation can depend both on the scalar field itself and on its derivatives, encapsulating a wide variety of scalar-tensor theories. This generalisation also leads to new and richer phenomenology, explaining some of the features found in previously studied models. We present the background equations and perform a detailed dynamical analysis, from where new disformal fixed points emerge, that translate into novel cosmological features. These include early scaling regimes between the coupled species and broader stability parameter regions. However, viable cosmological models seem to have suppressed disformal late-time contributions.