Weakly dynamic dark energy via metric-scalar couplings with torsion

TL;DR

This paper explores a non-minimally coupled scalar field with torsion as a model for weakly dynamic dark energy, providing explicit cosmological solutions and constraints consistent with current observations and local gravity tests.

Contribution

It introduces a novel scalar-torsion coupling framework for dark energy, deriving explicit solutions and observational bounds, and highlights differences from a cosmological constant.

Findings

Dark energy can be weakly dynamic with torsion-scalar couplings.

Explicit cosmological solutions are consistent with observational data.

Upper bounds on torsion parameters and large Brans-Dicke parameter are established.

Abstract

We study the dynamical aspects of dark energy in the context of a non-minimally coupled scalar field with curvature and torsion. Whereas the scalar field acts as the source of the trace mode of torsion, a suitable constraint on the torsion pseudo-trace provides a mass term for the scalar field in the effective action. In the equivalent scalar-tensor framework, we find explicit cosmological solutions representing dark energy in both Einstein and Jordan frames. We demand the dynamical evolution of the dark energy to be weak enough, so that the present-day values of the cosmological parameters could be estimated keeping them within the confidence limits set for the standard $\L$CDM model from recent observations. For such estimates, we examine the variations of the effective matter density and the dark energy equation of state parameters over different redshift ranges. In spite of being weakly dynamic, the dark energy component differs significantly from the cosmological constant, both in characteristics and features, for e.g. it interacts with the cosmological (dust) fluid in the Einstein frame, and crosses the phantom barrier in the Jordan frame. We also obtain the upper bounds on the torsion mode parameters and the lower bound on the effective Brans-Dicke parameter. The latter turns out to be fairly large, and in agreement with the local gravity constraints, which therefore come in support of our analysis.