arXiv subjects

J. Tossa

Publications and source records attributed to J. Tossa.

At least 19 recordsLinked to original sources

arXiv2019

Inflationary scenario driven by type IV singularity in $f(T)$ gravity

In this paper, we investigate the effects of Type IV singularity through $f(T)$ gravity description of inflationary universe, where $T$ denotes the torsion scalar. With the Friedmann equations of the theory, we reconstruct a $f(T)$ model according to a given Hubble rate susceptible to describe the inflationary era near the type IV singularity. Moreover, we calculate the Hubble flow parameters in order to determine the dynamical evolution of the cosmological system. The results show that some of the Hubble flow parameters are small near the Type IV singularity and become singular at Type IV Singularity, indicating that a dynamical instability of the cosmological system occurs a that point. This means that the dynamical cosmological evolution up to that point, ceases to be the final attractor since the system is abruptly interrupted. Furthermore, by considering the $f(T)$ trace anomaly equation and the slow-roll conditions, we deal with the de Sitter inflationary description of the reconstructed model. As results, the model leads to a conditional instability, view as the source of the graceful exit from inflation. Our theoretical $f(T)$ description based on slow-roll parameters not only confirms some observational data on spectral index and the scalar-to-tensor ratio from Planck data and BICEP$2$/Keck-Array data, but also shows the property of $f(T)$ gravity in describing the early and late-time evolution of our universe.

gr-qc↗

arXiv2018

New Traversable Wormholes Solutions in $f(T)$ Gravity

In this paper we search for dynamical traversable wormhole solution in the modified $f(T)$ theory of gravity, $T$ being the torsion scalar. For such wormhole, the time dependence is inserted in the static traversable wormhole metric of Morris and Thore. Two set of tetrads are adopted: the diagonal and the non-diagonal tetrads. The diagonal set of tetrads constrains and reduces $f(T)$ model to teleparallel theory where usual solutions have been found. With diagonal set of tetrads, free from the teleparallel theory constraint, our results show that the existence of traversable wormhole is possible only for non-dynamical spacetime metric, i.e, static traversable wormhole solutions. Moreover we take into account energy condition analysis and the results show that the violation of NEC is not determinant for existence of static traversable wormhole solutions.

physics.gen-ph↗

arXiv2018

Cosmological Study of Autonomous Dynamical Systems in Modified Tele-Parallel Gravity

Cosmological approaches of autonomous dynamical system in the framework of $f(T)$ gravity are investigated in this paper. Our methods applied to flat Friedmann-Robertson-Walker equations in $f(T)$ gravity, consist to extract dynamical systems whose time-dependence is contained in a single parameter $m$ depending on the Hubble rate of Universe and its second derivative. In our attempt to investigate the autonomous aspect of the dynamical systems reconstructed in both vacuum and non-vacuum $f(T)$ gravities, two values of the parameter $m$ have been considered for our present analysis. In the so-called quasi-de Sitter inflationary era ($m\simeq0$), the corresponding autonomous dynamical systems provide stable de Sitter attractors and unstable de Sitter fixed points. Especially in the vacuum $f(T)$ gravity, the approximate form of the $f(T)$ gravity near the stable and the unstable de Sitter fixed points has been performed. The matter dominated era case $(m=-\frac{9}{2})$ leads to unstable fixed points confirming matter dominated era or not, and stable attractor fixed point describing dark energy dominated era. Another subtlety around the stable fixed point obtained at matter dominated case in the non-vacuum $f(T)$ gravity is when the dark energy dominated era is reached, at the same time, the radiation perfect fluid dominated succumbs.

gr-qc↗

arXiv2017

Holographic dark energy model in unimodular $f(T)$ gravity

The present work deals with holographic dark energy in the context of unimodular $f(T)$ gravity, which is a modification of teleparallel gravity. We develop the general reconstruction procedure of the $f(T)$ form that can yield the holographic feature of the dark energy. We fit the reconstructed model with the $H(z)$ data and our results show a perfect agreement with the WMAP9 cosmological observational data, at least for the range $-1.10\leq ω_V \leq -1.05$. We investigate the consistency of the reconstructed model by studying its stability against linear gravitational and matter perturbations, fixing $ω_V$ to $-1.05$. The model presents stability for both de Sitter and power-law solutions and we conclude that it is a good candidate as alternative viable model for characterizing holographic dark energy.

physics.gen-ph↗

arXiv2017

$f(T)$ gravity and energy distribution in Landau-Lifshitz prescription

We investigate in this paper the Landau-Lifshitz energy distribution in the framework of $f(T)$ theory view as a modified version of Teleparallel theory. From some important Teleparallel theory results on the localization of energy, our investigations generalize the Landau-Lifshitz prescription from the computation of the energy-momentum complex to the framework of $f (T)$ gravity as it is done in the modified versions of General Relativity. We compute the energy density in the first step for three plane symmetric metrics in vacuum. We find for the second metric that the energy density vanishes independently of $f (T)$ models. These metrics provide results in perfect agreement with those mentioned in literature. In the second step the calculations are performed for the Cosmic String Spacetime metric. It results that the energy distribution depends on the mass $M$ of cosmic string and it is strongly affected by the parameter of the considered $f (T)$ quadratic model.

physics.gen-ph↗

arXiv2016

Strong Magnetic field effects on Neutron Stars within $f(T)$ theory of gravity

We investigate in this paper the structures of neutron stars under the strong magnetic field in the framework of $f(T)$ gravity where $T$ denotes the scalar torsion. The TOV equations in this theory of gravity have been considered and numerical resolution of these equations has been performed within perturbative approach taking into account the equation of state of neutron dense matter in magnetic field. We simplify the problem by considering the very strong magnetic field which affects considerably the dense matter; and for quadratic and cubic corrections to Teleparallel term, one finds that the mass of neutron stars can increase for different values of the perturbation parameter. The deviation from Teleparallel for different values of magnetic field is found out and this feature is very appreciable in the case of cubic correction. Our results are related to the hadronic particles description with very small hyperon contributions and the mass-radius evolution is consistency with the observational data.

physics.gen-ph↗

arXiv2016

Exploring stable models in $f(R; T; R_{μν} T^{μν})$ gravity

We examine in this paper the stability analysis in $f(R; T; R_{μν}T^{μν})$ modified gravity, where $R$ and $T$ are the Ricci scalar and the trace of the energy-momentum tensor, respectively. By considering the flat Friedmann universe, we obtain the corresponding generalized Friedmann equations and we evaluate the geometrical and matter perturbation functions. The stability is developed using the de Sitter and power-law solutions. We search for application the stability of two particular cases of $f(R; T; R_{μν}T^{μν})$ model by solving numerically the perturbation functions obtained.

gr-qc↗

arXiv2016

Perfect fluid and F(T) gravity descriptions of inflationary universe and comparison with obervational data

We describe in this paper the observables of inflationary models, in particular the spectrum index of torsion scalar perturbations, the tensor-to-scalar ratio, and the running of the spectral index, in the framework of perfect fluid models and F(T) gravity theories through the reconstruction methods. Then, our results on the perfect fluid and F(T) gravity theories of inflation are compared with recent cosmological observations such as the Planck satellite and BICEP2 experiment. Ours studies prove that the perfect fluid and F(T) gravity models can reproduce the inflationary universe consistent above all with the Planck data. We have reconstructed several models and considered others which give the best fit values compatible with the spectral index of curvature perturbations, the tensor-to-scalar ratio, and the running of the spectral index within the allowed ranges suggested by the Planck and BICEP2 results.

gr-qc↗

arXiv2016

Stability and Space Phase Analysis in f(R) theory with Generalized Exponential model

We have studied in this paper, the stability of dynamical system in $f(R)$ gravity. We have considered the $f(R)$ $γ$-gravity and explored its dynamical analysis. We found six critical points among which only one describes an universe fulled of both matter and dominated dark energy. It's shown that these critical points presents specific phase spaces described by the corresponding fluids. Furthermore, we've investigated the stability conditions of these critical points and find that theses conditions are dependent of the model parameters. We also study the stability of a new power-law $f_\ast(R)$ model with de Sitter and power law solutions.

gr-qc↗

arXiv2016

Unimodular f(T) gravity

We reconstruct the geometrical $f(T)$ actions in the framework of unimodular $f(T)$ gravity. The unimodular $f(T)$ gravity yields stunning properties related to the generalized Friedmann equations. Indeed, it has been found that depending on the form of the Friedmann equations, the Lagrange multipliers may or not depend on the time parameter $τ$. Moreover we find that the reconstruction of $f(T)$ functions can be easily performed in general, not depending on a given scale factor, or can determine a particular way, depending on a given scale factor, in the vacuum. It is noted that the reconstruction of a general action joins is consistent to the unimodular gravity for the constant $Λ$

gr-qc↗

arXiv2016

Interactions of some fluids with dark energy in f(T) theory

We investigate the interaction of the dark energy with some fluids filling the universe in the framework of $f(T)$ theory, where $T$ denotes the torsion scalar, searching for the associated gravitational actions. Dark energy is assumed to be of gravitational origin. The interaction of dark energy and baryonic matter is considered resulting in a decay of the energy density of the ordinary matter, where universe appears as driven by cosmological constant. Furthermore we consider the interaction of dark energy with Van Der Waals fluid and in this regard the universe is seemed plunging into a phantom phase. Finally, the interaction of the dark energy with Chaplygin gas is studied, leading to a universe dominated by the cosmological constant.

physics.gen-ph↗

arXiv2015

Geodesic Deviation Equation in $Λ$CDM $f(T,\mathcal{T})$ gravity

The geodesic deviation equation has been investigated in the framework of $f(T,\mathcal{T})$ gravity, where $T$ denotes the torsion and $\mathcal{T}$ is the trace of the energy-momentum tensor, respectively. The FRW metric is assumed and the geodesic deviation equation has been established following the General Relativity approach in the first hand and secondly, by a direct method using the modified Friedmann equations. Via fundamental observers and null vector fields with FRW background, we have generalized the Raychaudhuri equation and the Mattig relation in $f(T,\mathcal{T})$ gravity. Furthermore, we have numerically solved the geodesic deviation equation for null vector fields by considering a particular form of $f(T,\mathcal{T})$ which induces interesting results susceptible to be tested with observational data.

gr-qc↗

arXiv2015

$f(T,\mathcal{T})$ Cosmological Models in Phase Space

In this paper we explore $f(T, \mathcal{T})$, where $T$ and $\mathcal{T}$ denote the torsion scalar and the trace of the energy-momentum tensor respectively. We impose the covariant conservation to the energy-momentum tensor and obtain a cosmological $f(T, \mathcal{T})$ respectively. We impose the covariant conservation to the energy-momentum tensor and obtain a cosmological $f(T, \mathcal{T})$ model. Then, we study the stability of the obtained model for power-law and de Sitter solutions and our result show that the model can be stable for some values of the input parameters, for both power-law and de Sitter solutions.

physics.gen-ph↗

arXiv2015

Cosmological Evolution in f(R,T) theory with Collisional Matter

We study the evolution of the cosmological parameters, namely, the deceleration parameter $q(z)$ and the parameter of effective equation of state in a universe contains, besides the ordinary matter and dark energy, a self-interacting (collisional matter), in the generalized $f(R,T)$ theory of gravity, where $R$ and $T$ are the curvature scalar and the trace of the energy-momentum tensor, respectively. We use the generalized FRW equations the equation of continuity and obtain a differential equation of second order in $H(z)$, and solve it numerically for studying the evolution of the cosmological parameters. Two $f(R,T)$ models are considered and the results with collisional matter are compared with the ones of the $Λ$CDM model, and also with the model where there exists only non-collisional matter. The curves show that the models are acceptable because the values found for $w_{eff}$ are consistent with the observational data.

gr-qc↗

arXiv2015

Realistic f(T) model describing the de Sitter epoch of the dark energy dominated universe

We consider an exponential model within the so-called f(T) theory of gravity, where $T$ denotes the torsion scalar. We focus our work on a cosmological feature of such a model, checking whether it may describe the de Sitter stage of the current universe through the analysis of the redshift z. Our results shows that the model reproduces the de Sitter stage only for low-redshifts, where the perturbation function goes toward zero as the low values of the redshift are reached, whereas the effective parameter of equation of state goes to -1, which is the expected behavior for any model able to reproduce de Sitter stage.

gr-qc↗

arXiv2015

Geodesic Deviation Equation in $f (R,T)$ Gravity

In this paper, we investigate the modified Geodesic Deviation Equation (GDE) in the framework of $f(R,T)$ theory of gravity where $R$ and $T$ are the curvature scalar and the trace of the energy-momentum tensor, respectively, using the FLRW background. In this way, we obtain the GR equivalent (GDE) in $f(R,T)$ metric formalism. We also extend our work to the generalization of the Matting relation and perform the numerical analysis with GDE for null vector.

gr-qc↗

arXiv2015

From the early to the late time universe within $f(T,\mathcal{T})$ gravity

In this paper we perform the reconstruction scheme of the gravitational action within $f(T,\mathcal{T})$ gravity, where $T$ and $\mathcal{T}$ denote the torsion scalar and the trace of the energy momentum tensor, respectively. We particularly focus our attention on the case where the algebraic function $f(T,\mathcal{T})$ is decomposed as a sum of two functions $f_1(T)$ and $f_2(\mathcal{T})$, i.e, $f(T,\mathcal{T})=f_{1}(T)+f_{2}(\mathcal{T})$. The description is essentially based on the scale factor and then, we consider two interesting and realistic expressions of this parameter and reconstruct the action corresponding to each phase of the universe. Our results show that some $f(T,\mathcal{T})$ models are able to describe the evolution of the universe from the inflation phase to the late time dark energy dominated phase.

gr-qc↗

arXiv2014

Cosmological viable f(R,T) dark energy model: dynamics and stability

In this paper we undertake the modified theory of gravity f(R,T) where R and T are the Ricci scalar and the trace of the energy momentum tensor, respectively. Imposing the conservation of the energy momentum tensor, we obtain a model about what dynamics and stability are studied. The stability is developed using the de Sitter and power-law solutions. The results show that the model presents stability for both the de Sitter and power-law solutions. Regarding the dynamics, cosmological solutions are obtained by integrating the background equations for both the low-redshift and High-redshift regimes and are consistent with the observational data.

gr-qc↗