Matter Bounce Cosmology with the f(T) Gravity

TL;DR

This paper explores how f(T) gravity can produce bouncing cosmologies that avoid the Big Bang singularity, analyzing perturbations and their observational implications.

Contribution

It demonstrates that f(T) gravity can realize matter bounce scenarios with distinctive perturbation features and discusses ways to reconcile predictions with observations.

Findings

f(T) gravity enables bouncing cosmologies avoiding singularities

Scalar perturbations exhibit a background-dependent sound speed

Primordial power spectrum is scale-invariant but has a high tensor-to-scalar ratio

Abstract

We show that the f(T) gravitational paradigm, in which gravity is described by an arbitrary function of the torsion scalar, can provide a mechanism for realizing bouncing cosmologies, thereby avoiding the Big Bang singularity. After constructing the simplest version of an f(T) matter bounce, we investigate the scalar and tensor modes of cosmological perturbations. Our results show that metric perturbations in the scalar sector lead to a background-dependent sound speed, which is a distinguishable feature from Einstein gravity. Additionally, we obtain a scale-invariant primordial power spectrum, which is consistent with cosmological observations, but suffers from the problem of a large tensor-to-scalar ratio. However, this can be avoided by introducing extra fields, such as a matter bounce curvaton.