arXiv subjects

M. J. S. Houndjo

Publications and source records attributed to M. J. S. Houndjo.

At least 37 records · Page 2Linked to original sources

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↗

arXiv2016

Higher-Derivative $f(R,\Box R, T)$ Theories of Gravity

In literature there is a model of modified gravity in which the matter Lagrangian is coupled to the geometry via trace of the stress-energy momentum tensor $T=T_μ^μ$. This type of modified gravity is called as $f(R,T)$ in which $R$ is Ricci scalar $R=R_μ^μ$. We extend manifestly this model to include the higher derivative term $\Box R$. We derived equation of motion (EOM) for the model by starting from the basic variational principle. Later we investigate FLRW cosmology for our model. We show that de Sitter solution is unstable for a generic type of $f(R,\Box R, T)$ model. Furthermore we investigate an inflationary scenario based on this model. A graceful exit from inflation is guaranteed in this type of modified gravity.

gr-qc↗

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

Tolman-Oppenheimer-Volkoff Equations and their implications or the structures of relativistic Stars in f(T) gravity

We investigate in this paper the structures of neutron and quark stars in f(T) theory of gravity where T denotes the torsion scalar. Attention is attached to the TOV type equations of this theory and numerical integrations of these equations are performed with suitable EoS. We search for the deviation of the mass-radius diagrams for power-law and exponential type correction from the TT gravity. Our results show that for some values of the input parameters appearing in the considered models, f(T) theory promotes more the structures of the relativistic stars, in consistency with the observational data.

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

Spherically symmetric solutions of light Galileon

We have been studied the model of light Galileon with translational shift symmetry $ϕ\to ϕ+c$. The matter Lagrangian is presented in the form $\mathcal{L}_ϕ= -η(\partial ϕ)^2+βG^{μν}\partial_μϕ\partial_νϕ$. We have been addressed two issues: the first is that, we have been proven that, this type of Galileons belong to the modified matter-curvature models of gravity in type of $f(R,R^{μν}T_{μν}^m)$. Secondly, we have been investigated exact solution for spherically symmetric geometries in this model. We have been found an exact solution with singularity at $r=0$ in null coordinates. We have been proven that the solution has also a non-divergence current vector norm. This solution can be considered as an special solution which has been investigated in literature before, in which the Galileon's field is non-static (time dependence). Our scalar-shift symmetrized Galileon has the simple form of $ϕ=t$, which it is remembered by us dilaton field.

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↗

arXiv2015

Isotropic turbulence in the dark fluid universe with inhomogeneous equation of state

We investigate the turbulence effect in dark fluid universe with linear inhomogeneous equation of state. Attention is attached to two physical situations. First, we perform the perturbative analysis of turbulence and check its effects around the Big Rip. Later, treating the turbulence energy density as a part of total dark fluid, we study the stability of the system. The result shows that the stability is achieving as the energy density of turbulence decreases, changing into heat (the radiation), in perfect agreement with the avoidance of the Big Rip.

gr-qc↗

arXiv2014

Bianchi type-I, type-III and Kantowski-Sachs solutions in f(T) gravity

In the context of modified tele-parallel theory of gravity, we undertake cosmological anisotropic models and search for their solutions. Within a suitable choice of non-diagonal tetrads, the decoupled equations of motion are obtained for Bianchi-I, Bianchi-III and Kantowski-Sachs models, from which we obtain the correspondent solutions. By the way, energy density and pressures are also obtained, showing, as an important result, that our universe may live a quintessence like universe even still anisotropic models are considered.

gr-qc↗

arXiv2014

Inhomogeneous Universe in f(T) Theory

We obtain the equations of motions of the $f(T)$ theory considering the Lemaître-Tolman-Bondi's metric for a set of diagonal and non-diagonal tetrads. In the case of diagonal tetrads the equations of motion of the $f(T)$ theory impose a constant torsion or the same equations of the General Relativity, while in the case of non-diagonal set the equations are quite different from that obtained in GR. We show a simple example of an universe dominated by the matter for the two cases. The comparison of the mass in the non-diagonal case shows a sort of increased with respect to the diagonal one. We also perform two examples for the non-diagonal case. The first concerns a black hole solution of type Sshwarzschild which presents a temperature higher than that of Schwarzschild, and a black hole in a dust-dominated universe.

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↗

arXiv2013

LCDM Model in f(T) Gravity: Reconstruction, Thermodynamics and Stability

We investigate some cosmological features of the LCDM model in the framework of the generalized teleparallel theory of gravity f(T) where T denotes the torsion scalar. Its reconstruction is performed giving rise to an integration constant Q and other input parameters according to which we point out more analysis. Thereby, we show that for some values of this constant, the first and second laws of thermodynamics can be realized in the equilibrium description, for the universe with the temperature inside the horizon equal to that at the apparent horizon. Moreover, still within these suitable values of the constant, we show that the model may be stable using the de Sitter and Power-Law cosmological solutions.

gr-qc↗

arXiv2013

Charged Black Holes in Generalized Teleparallel Gravity

In this paper we investigate charged static black holes in 4D for generalized teleparallel models of gravity, based on torsion as the geometric object for describing gravity according to the equivalence principle. As a motivated idea, we introduce a set of non-diagonal tetrads and derive the full system of non linear differential equations. We prove that the common Schwarzschild gauge is applicable only when we study linear f(T) case. We reobtain the Reissner-Nordstrom-de Sitter (or RN-AdS) solution for the linear case of f(T) and perform a parametric cosmological reconstruction for two nonlinear models. We also study in detail a type of the no-go theorem in the framework of this modified teleparallel gravity.

gr-qc↗

arXiv2013

A Type of Levi-Civita's Solution in Modified Gauss-Bonnet Gravity

In this letter we obtain an exact solution for cylindrically symmetric modified Gauss Bonnet gravity. This metric is a generalization of the vacuum solution of the Levi-Civita in the general relativity. It describes an isotropic perfect fluid one parameter family of the gravitational configurations which can be interpreted as the exterior metric of a cosmic string. By setting the Gauss-Bonnet coupling parameter to zero, we recover the vacuum solution in the Einstein gravity as well.

gr-qc↗