Cosmic acceleration in non-flat $f(T)$ cosmology

TL;DR

This paper investigates non-flat $f(T)$ cosmological models, analyzing their dynamics with observational data, and finds that they can mimic $ ext{Lambda}$CDM while allowing for non-zero spatial curvature and crossing the phantom divide.

Contribution

It introduces and tests two specific non-flat $f(T)$ models against observational data, highlighting their ability to fit late-time cosmology and exhibit phantom crossing.

Findings

Non-zero spatial curvature is favored at 1$\sigma$ level.

Both models fit late-time data well, similar to $ ext{Lambda}$CDM.

Polynomial $f(T)$ model predicts an effective de-Sitter phase.

Abstract

We study $f(T)$ cosmological models inserting a non-vanishing spatial curvature and discuss its consequences on cosmological dynamics. To figure this out, a polynomial $f(T)$ model and a double torsion model are considered. We first analyze those models with cosmic data, employing the recent surveys of Union 2.1, baryonic acoustic oscillation and cosmic microwave background measurements. We then emphasize that the two popular $f(T)$ models enable the crossing of the phantom divide line due to dark torsion. Afterwards, we compute numerical bounds up to 3-$\sigma$ confidence level, emphasizing the fact that $\Omega_{k0}$ turns out to be non-compatible with zero at least at 1$\sigma$. Moreover, we underline that, even increasing the accuracy, one cannot remove the degeneracy between our models and the $\Lambda$CDM paradigm. So that, we show that our treatments contain the concordance paradigm and we analyze the equation of state behaviors at different redshift domains. We also take into account gamma ray bursts and we describe the evolution of both the $f(T)$ models with high redshift data. We calibrate the gamma ray burst measurements through small redshift surveys of data and we thus compare the main differences between non-flat and flat $f(T)$ cosmology at different redshift ranges. We finally match the corresponding outcomes with small redshift bounds provided by cosmography. To do so, we analyze the deceleration parameters and their variations, proportional to the jerk term. Even though the two models well fit late-time data, we notice that the polynomial $f(T)$ approach provides an effective de-Sitter phase, whereas the second $f(T)$ framework shows analogous results compared with the $\Lambda$CDM predictions.