Phase Space description of Nonlocal Teleparallel Gravity

TL;DR

This paper investigates the dynamics of nonlocal teleparallel gravity using phase space analysis, deriving autonomous systems, exploring fixed points, and examining the stability of de Sitter solutions in various cosmological scenarios.

Contribution

It introduces a phase space framework for nonlocal $f(T)$ gravity, analyzes fixed points and stability, and explores conditions for stable de Sitter solutions.

Findings

Stable de Sitter solutions can exist even in vacuum spacetime.

The autonomous dynamical system approach reveals fixed points and attractors.

The role of the gauge function $ ext{eta}$ in cosmological solutions is clarified.

Abstract

We study cosmological solutions in nonlocal teleparallel gravity or $f(T)$ theory, where $T$ is the torsion scalar in teleparallel gravity. This is a natural extenstion of the usual teleparallel gravity with nonlocal terms. In this work the phase space portrait proposed to describe the dynamics of an arbitrary flat, homogeneous cosmological background with a number of matter contents, both in early and late time epochs. The aim was to convert the system of the equations of the motion to a first order autonomous dynamical system and to find fixed points and attractors using numerical codes. For this purpose, firstly we derive effective forms of cosmological field equations describing the whole cosmic evolution history in a homogeneous and isotropic cosmological background and construct the autonomous system of the first order dynamical equations. In addition, we investigate the local stability in the dynamical systems called "the stable/unstable manifold" by introducing a specific form of the interaction between matter, dark energy, radiation and a scalar field. Furthermore, we explore the exact solutions of the cosmological equations in the case of de Sitter spacetime. In particular, we examine the role of an auxiliary function called "gauge" $\eta$ in the formation of such cosmological solutions and show whether the de Sitter solutions can exist or not. Moreover, we study the stability issue of the de Sitter solutions both in vacuum and non-vacuum spacetimes. It is demonstrated that for nonlocal $f(T)$ gravity, the stable de Sitter solutions can be produced even in vacuum spacetime.