Teleparallel quintessence with a nonminimal coupling to a boundary term

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 1⁄4 2e ∂μðeTμÞ. This is inspired by the relation R 1⁄4 −T þ 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 analyze 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.