Interacting quintessence from a variational approach Part II: derivative couplings

TL;DR

This paper introduces a novel variational framework for modeling interacting quintessence with matter, allowing derivative couplings at the Lagrangian level, leading to rich cosmological phenomenology including late-time acceleration and phantom crossing.

Contribution

It develops a new variational approach for derivative couplings in quintessence models, expanding previous algebraic coupling frameworks and exploring their cosmological implications.

Findings

Models exhibit dark energy dominated late-time attractors.

Early matter-dominated epochs are present in the models.

Possible dynamical crossing of the phantom barrier is observed.

Abstract

We consider an original variational approach for building new models of quintessence interacting with dark or baryonic matter. The coupling is introduced at the Lagrangian level using a variational formulation for relativistic fluids, where the interacting term generally depends on both the dynamical degrees of freedom of the theory and their spacetime derivatives. After deriving the field equations from the action, we consider applications in the context of cosmology. Two simple models are studied using dynamical system techniques showing the interesting phenomenology arising in this framework. We find that these models contain dark energy dominated late time attractors with early time matter dominated epochs and also obtain a possible dynamical crossing of the phantom barrier. The formulation and results presented here complete and expand the analysis exposed in the first part of this work, where only algebraic couplings, without spacetime derivatives, were considered.