Scalar field unification of interacting viscous dark fluid from a geometrical scalar-tensor theory of gravity

TL;DR

This paper explores a scalar-tensor gravity theory where a single scalar field unifies viscous dark fluid and dark energy, providing analytic models and constraining parameters with Planck 2018 data.

Contribution

It introduces a novel scalar-tensor model with a non-canonical kinetic term that unifies viscous dark fluid and dark energy within a geometrical framework.

Findings

Derived analytic scalar field and potential models for different equations of state.

Constrained model parameters using Planck 2018 observational data.

Showed the scalar viscosity depends on Hubble and deceleration parameters.

Abstract

We investigate, in the framework of a recently introduced new class of invariant geometrical scalar-tensor theory of gravity, the possibility that a viscous dark fluid can be described in a unified manner by a single scalar field. Thus we developed a model in which both the metric tensor and the scalar field have geometrical origin. The scalar field is characterized by a non-canonical kinetic term and the scalar viscosity of the dark fluid appears as soon the kinetic energy of the scalar field is no longer canonical. The scalar viscosity is considered as a function of the Hubble and the deceleration parameters. To illustrate the formalism we have considered two cases: a constant and a thermodynamic equation of state parameters. In the both cases we obtain analytic representations for the scalar field and their respective potentials. We delimit free parameters by comparing with some Planck 2018 results.