Growth factor in f(T) gravity

We derive the evolution equation of growth factor for the matter over-dense perturbation in $f(T)$ gravity. For instance, we investigate its behavior in power law model at small redshift and compare it to the prediction of $\Lambda$CDM and dark energy with the same equation of state in the framework of Einstein general relativity. We find that the perturbation in $f(T)$ gravity grows slower than that in Einstein general relativity if \p f/\p T>0 due to the effectively weakened gravity.Comment: 15 pages,1 figure; v2,typos corrected; v3, discussions added, accepted by JCA

Notes on f(T)f(T) Theories

The cosmological models based on teleparallel gravity with nonzero torsion are considered. To investigate the evolution of this theory, we consider the phase-space analysis of the $f(T)$ theory. It shows when the tension scalar can be written as an inverse function of $x$ where $x=\rho_{e}/(3m_{pl}^{2}H^{2})$ and $T=g(x)$, the system is an autonomous one. Furthermore,the $\omega_{e}-\omega'_{e}$ phase analysis is given out. We perform the dynamical analysis for the models $f(T)=\beta T\ln(T/T_{0})$ and $f(T)=\alpha m_{pl}^{2}(-T/m_{pl}^{2})^{n}$ particularly. We find that the universe will settle into de-Sitter phase for both models. And we have examined the evolution behavior of the power law form in the $\omega_{ep}-\omega'_{ep}$ plane.Comment: 13 pages, 2 figure

Observational Constraints on Teleparallel Dark Energy

We use data from Type Ia Supernovae (SNIa), Baryon Acoustic Oscillations (BAO), and Cosmic Microwave Background (CMB) observations to constrain the recently proposed teleparallel dark energy scenario based on the teleparallel equivalent of General Relativity, in which one adds a canonical scalar field, allowing also for a nonminimal coupling with gravity. Using the power-law, the exponential and the inverse hyperbolic cosine potential ansatzes, we show that the scenario is compatible with observations. In particular, the data favor a nonminimal coupling, and although the scalar field is canonical the model can describe both the quintessence and phantom regimes.Comment: 19 pages, 6 figures, version accepted by JCA

Parametrization for the Scale Dependent Growth in Modified Gravity

We propose a scale dependent analytic approximation to the exact linear growth of density perturbations in Scalar-Tensor (ST) cosmologies. In particular, we show that on large subhorizon scales, in the Newtonian gauge, the usual scale independent subhorizon growth equation does not describe the growth of perturbations accurately, as a result of scale-dependent relativistic corrections to the Poisson equation. A comparison with exact linear numerical analysis indicates that our approximation is a significant improvement over the standard subhorizon scale independent result on large subhorizon scales. A comparison with the corresponding results in the Synchronous gauge demonstrates the validity and consistency of our analysis.Comment: 10 pages, 5 figures. Minor modifications and references added to match published versio