Interacting quintessence from a variational approach Part I: algebraic couplings

TL;DR

This paper introduces a variational approach to model interacting quintessence with matter, leading to new phenomenology at different scales and revealing diverse cosmological solutions including late-time acceleration and scaling behaviors.

Contribution

It presents a novel variational framework for constructing interacting quintessence models with algebraic couplings at the Lagrangian level, enabling exploration of new cosmological phenomena.

Findings

Models exhibit dark energy dominated late-time attractors.

Presence of scaling solutions with matter epochs.

Potential for inflationary origins in early universe.

Abstract

We present a new approach to build models of quintessence interacting with dark or baryonic matter. We use a variational approach for relativistic fluids to realize an effective description of matter fields at the Lagrangian level. The coupling is introduced directly in the action by considering a single function mixing the dynamical degrees of freedom of the theory. The resulting gravitational field equations are derived by variations with respect to the independent variables. New interesting phenomenology can be obtained at both small scales, where new screening mechanisms for scalar fields can be realized, and large scales, where one finds an original and rich class of interacting quintessence models. The background cosmology of two of these models is studied in detail using dynamical system techniques. We find a variety of interesting results: for instance, these models contain dark energy dominated late time attractors and scaling solutions, both with early time matter dominated epochs and a possible inflationary origin. In general this new approach provides the starting point for future in depth studies on new interacting quintessence models.