Teleparallel quintessence with a nonminimal coupling to a boundary term

TL;DR

This paper introduces a novel teleparallel gravity model where a scalar field is nonminimally coupled to torsion and a boundary term, leading to late-time acceleration and possible phantom crossing without fine-tuning.

Contribution

It develops a new scalar-torsion boundary coupling model in teleparallel gravity, analyzing its cosmological dynamics and late-time acceleration solutions.

Findings

System evolves to a late-time accelerating attractor.

Possible dynamical crossing of the phantom barrier.

Model generalizes previous nonminimal coupling theories.

Abstract

We propose a new model in the teleparallel framework where we consider a scalar field nonminimally coupled to both the torsion $T$ and a boundary term given by the divergence of the torsion vector $B=\frac{2}{e}\partial_\mu (eT^\mu)$. This is inspired by the relation $R=-T+B$ between the Ricci scalar of general relativity and the torsion of teleparallel gravity. This theory in suitable limits incorporates both the nonminimal coupling of a scalar field to torsion, and the nonminimal coupling of a scalar field to the Ricci scalar. We analyse the cosmology of such models, and we perform a dynamical systems analysis on the case when we have only a pure coupling to the boundary term. It is found that the system generically evolves to a late time accelerating attractor solution without requiring any fine tuning of the parameters. A dynamical crossing of the phantom barrier is also shown to be possible.