Non-minimal Torsion-matter Coupling Research Articles

Non-minimal torsion-matter coupling and wormhole solutions

Taking into account various energy density models in the framework of torsion-based modified theory, some wormhole solutions are derived and studied. We use a non-minimal coupling between matter and torsion in order to construct the wormhole geometry for constant, exponential and Lorentzian energy density models. Two sets of torsion dependent models, including (i) teleparalell case with linear forms of torsion scalar and (ii) a [Formula: see text] gravity with quadratic form of torsion scalar, have been considered throughout this paper. Our study shows that additional terms to the Einstein field equations, due to consider modified gravity, give us the opportunity of obtaining wormhole solutions which may be supported by baryonic sources. We also check the equilibrium phase of the wormhole solutions using anisotropic and hydrostatic forces. The details of the obtained results depend on the numerical values of the free parameters that the function [Formula: see text] holds.

Growth of matter overdensities in non-minimal torsion-matter coupling theories

We study the evolution of cosmological perturbations around a homogeneous and isotropic background in the framework of the non-minimal torsion-matter coupling extension of f(T) gravity. We are concerned with the effects of the non-minimal coupling term on the growth of matter overdensities. Under the quasi-static approximation, we derive the equation which governs the evolution of matter density perturbations, and it is shown that the effective gravitational coupling ‘constant’ acquires an additional contribution due to the non-minimal matter-torsion coupling term. In this way, this result generalizes those previously obtained for the growth of matter overdensities in the case of minimal f(T) gravity. In order to get a feeling of our results we apply them to the important case of a power-law coupling function, which we assume to be the responsible for the late-time accelerated expansion in the dark energy regime. Thereby, analytic solutions for the matter density perturbation equation in the regime of dark matter dominance and the dark energy epoch are obtained, along with a complete numerical integration of this equation. In particular, we show that this model predicts a growth index larger than those obtained for varLambda CDM model, indicating therefore a smaller growth rate. Concomitantly, we show that the model at hand is potentially capable in alleviating the existing sigma _{8}-tension, being that it can provide us a fsigma _{8} prediction which is sim 4–5% below the respective prediction of concordance model.

Towards realisticf(T)models with nonminimal torsion-matter coupling extension

Using the observation data of SNeIa, CMB and BAO, we establish two concrete $f(T)$ models with nonminimal torsion-matter coupling extension. We study in detail the cosmological implication of our models and find they are successful in describing the observation of the Universe, its large scale structure and evolution. In other words, these models do not change the successful aspects of $\Lambda$CDM scenario under the error band of fitting values as describing the evolution history of the Universe including radiation-dominated era, matter-dominated era and the present accelerating expansion. Meanwhile, the significant advantage of these models is that they could avoid the cosmological constant problem of $\Lambda$CDM. A joint analysis is performed by using the data of CMB+BAO+JLA, which leads to $\Omega_{m0}=0.255\pm 0.010, \Omega_{b0}h^2=0.0221\pm 0.0003$ and $H_0=68.54\pm 1.27$ for model I and $\Omega_{m0}=0.306\pm 0.010, \Omega_{b0}h^2=0.0225\pm 0.0003$ and $H_0=60.97\pm 0.44$ for model II at 1$\sigma$ confidence level. The evolution of the decelaration parameter $q(a)$ and the effective equation of state $w_{DE}(a)$ are displayed. Furthermore, The resulted age of the Universe from our models is consistent with the ages of the oldest globular clusters. As for the fate of the Universe, model I results in a de Sitter accelerating phase while model II appears a power-law one, even though $w_{DE0}< -1$ makes model I look like a phantom at present time.

A spherically symmetric null tetrads in non-minimal torsion-matter coupling extension of f(T) gravity

We construct a null tetrad from a non-diagonal spherically symmetric vierbein field, involving two unknown functions of radial coordinate r. This null tetrad is applied to the equations of motion of non-minimal torsion-matter coupling extension off(T) gravity. Exact vacuum solution with two constants of integration is obtained. The scalar torsion related to this special solution is constant. The energy of this solution is calculated using the Euclidean continuation method and the known value is derived. We also calculate the thermodynamical quantities of charged Schwarzschild spacetime and investigate the validity of the first law of thermodynamics and quantum statistical relation.

Energy conditions in f(T) gravity with non-minimal torsion-matter coupling

The present paper examines the validity of energy bounds in a modified theory of gravity involving non-minimal coupling of torsion scalar and perfect fluid matter. In this respect, we formulate the general inequalities of energy conditions by assuming the flat FRW universe. For the application of these bounds, we particularly focus on two specific models that are recently proposed in literature and also choose the power law cosmology. We find the feasible constraints on the involved free parameters and evaluate their possible ranges graphically for the consistency of these energy bounds.

Nonminimal torsion-matter coupling extension off(T)gravity

We construct an extension of f(T) gravity with the inclusion of a non-minimal torsion-matter coupling in the action. The resulting theory is a novel gravitational modification, since it is different from both f(T) gravity, as well as from the non-minimal curvature-matter-coupled theory. The cosmological application of this new theory proves to be very interesting. In particular, we obtain an effective dark energy sector whose equation-of-state parameter can be quintessence or phantom-like, or exhibit the phantom-divide crossing, while for a large range of the model parameters the Universe results in a de Sitter, dark-energy-dominated, accelerating phase. Additionally, we can obtain early-time inflationary solutions too, and thus provide a unified description of the cosmological history.