Unified dark sectors in scalar-torsion theories of gravity

Abstract

We present a unified description of the matter and dark energy epochs, using a class of scalartorsion 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.

Teleparallel scalar-tensor gravity through cosmological dynamical systems

“…In this work we have explored the cosmological dynamics of dark energy through the prism of scalar-torsion gravity [36,37] in the context of power-law couplings with the kinetic term. In particular, we have studied one nontrivial extension of the recently proposed teleparallel analogue of Horndeski gravity [29].…”

“…The Friedmann equations in Eqs. (37,38) and Klein-Gordon equation in Eq. ( 39) directly lead to a set of autonomous equations for each of the models under investigation.…”

“…The division of the torsion scalar and boundary term means that a weaker Lovelock theorem is developed [27][28][29] where much more general theories that are second order can be produced such as f (T ) gravity [25]. f (T ) theories of gravity [30][31][32][33][34][35][36][37][38] emerged using the same rationale as f ( R) gravity [15,19,20] where the TEGR Lagrangian is generalized to an arbitrary function of the torsion scalar. These theories are generically second order and have shown promise in meeting some observational challenges in the literature [24,[39][40][41][42][43].…”