Unified dark sectors in scalar-torsion theories of gravity

TL;DR

This paper develops a scalar-torsion gravity model that unifies matter and dark energy epochs, providing analytic solutions and stable cosmological evolution including matter domination and late-time acceleration.

Contribution

It introduces a novel scalar-torsion framework with specific potentials, offering a stable, unified description of cosmic evolution with detailed dynamical analysis.

Findings

The model admits critical points with matter-like and dark energy-like behavior.

It predicts a universe transitioning from matter domination to accelerated expansion.

The scenario is free from instabilities at the perturbative level.

Abstract

We present a unified description of the matter and dark energy epochs, using a class of scalar-torsion theories. We provide a Hamiltonian description, and by applying Noether's theorem and by requiring the field equations to admit linear-in-momentum conservation laws we obtain two specific classes of scalar-field potentials. We extract analytic solutions and we perform a detailed dynamical analysis. We show that the system possesses critical points that correspond to scaling solutions in which the effective, total equation-of-state parameter is close to zero and points in which it is equal to the cosmological constant value $-1$. Therefore, during evolution, the Universe remains for sufficiently long times at the epoch corresponding to dust-matter domination, while at later times it enters the accelerated epoch and it eventually results in the de Sitter phase. Finally, in contrast to other unified scenarios, such as Chaplygin gas-based models as well as Horndeski-based constructions, the present scenario is free from instabilities and pathologies at the perturbative level.