Search

Rip cosmological models have been investigated in the framework of $f(T,\mathcal{T})$ theory of gravity, where $T$ denotes the torsion and $\mathcal{T}$ is the trace of the energy-momentum tensor. These phantom cosmological models revealed that at initial epoch a EoS parameter $\omega <-1$ and tends asymptotically at late phase to $-1$ $(\omega \rightarrow -1)$. On the other hand, Wormhole Solutions and Big Trip have been subject of an investigation. The wormhole throat radius $R(t)$ and the conditions to be satisfied so that produces the Big Trip phenomenon have been discussed., Comment: arXiv admin note: text overlap with arXiv:1904.01443 by other authors

We propose a stellar model under the $f(\mathbb{T},\mathcal{T})$ gravity following Mazur-Mottola's conjecture [Mazur (2001), Mazur (2004)] known as gravastar which is generally believed as a viable alternative to black hole. The gravastar consists of three regions, viz., (I) Interior region, (II) Intermediate shell region, and (III) Exterior region. The pressure within the interior core region is assumed to be equal to the constant negative matter-energy density which provides a constant repulsive force over the thin shell region. The shell is assumed to be made up of fluid of ultrarelativistic plasma and following the Zel'dovich's conjecture of stiff fluid [Zeldovich (1972)] it is also assumed that the pressure which is directly proportional to the matter-energy density according to Zel'dovich's conjecture, does cancel the repulsive force exerted by the interior region. The exterior region is completely vacuum and it can be described by the Schwarzschild solution. Under all these specifications we find out a set of exact and singularity-free solutions of the gravastar presenting several physically valid features within the framework of alternative gravity, namely $f(\mathbb{T},\mathcal{T})$ gravity [Harko (2014)], where the part of the gravitational Lagrangian in the corresponding action is taken as an arbitrary function of torsion scalar $\mathbb{T}$ and the trace of the energy-momentum tensor $\mathcal{T}$., Comment: 19 pages, 5 figures

We investigate alternative candidates to dark energy that can explain the current state of the universe in the framework of the generalized teleparallel theory of gravity $f(T)$ where $T$ denotes the torsion scalar. To achieve this, we carried out a series of reconstruction taking into account to the ordinary and entropy-corrected versions of the holographic and new agegraphic dark energy models. These models used as alternative to dark energy in the literature in order describe the current state of our universe. It is remarked that the models reconstructed indicates behaviors like phantom or quintessence models. Furthermore, we also generated the EoS parameters associated to entropy-corrected models and we observed a transition phase between quintessence state and phantom state as showed by recent observational data. We also investigated on the stability theses models and we created the $\{r-s\}$. The behavior of certains physical parameters as speed of sound and the Statefinder parameters are compatible with current observational data.

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., Comment: 12 pages. arXiv admin note: text overlap with arXiv:1510.04333, arXiv:1511.07586 by other authors

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., Comment: 12 pages and 6 figures

This paper is devoted to the reproduction of the gravitational baryogenesis epoch in the context of $f(R, T)$ theory of gravity, where $R$ and $T$ are respectively the curvature scalar and the trace of the energy-momentum tensor, respectively. It is assumed a minimal coupling between matter and gravity. In particular we consider the following two models, $f(R,T) = R +\alpha T + \beta T^2$ and $f(R,T) = R+ \mu R^2 + \lambda T$, with the assumption that the universe is filled by dark energy and perfect fluid where the baryon to entropy ratio during a radiation domination era is non-zero. We constrain the models with the cosmological gravitational baryogenesis scenario, highlighting the appropriate values of model's parameters compatible with the observation data of the baryon-entropy ratio., Comment: 6 pages, 2 figures

We investigate bouncing scenario in the modified $f(T)$ gravity, $T$ being the torsion scalar. Attention is attached to the reconstruction of $f(T)$ able to describe type IV singular bouncing evolution, where we adopt as assumption that the bouncing and type IV singularity points coincide. In the context of the reconstructed $f(T)$ model we calculate the Hubble slow-roll parameters in order to determine the dynamical evolution of the cosmological system under study. The results show that the Hubble slow-roll parameters become singular at the type IV singularity indicating a dynamical instability. Moreover we perform the stability analysis of the $f(T)$ gravity solution where, according to the obtained result, the type IV singularity point is a saddle point in agreement with the bounce scenario., Comment: 9 pages, 3 figures. arXiv admin note: text overlap with arXiv:1504.06866 by other authors

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., Comment: 25 pages and 5 figures. arXiv admin note: text overlap with arXiv:1711.02230 by other authors

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 $-1.10\leq \omega_V \leq -1.05$. We investigate the consistency of the reconstructed model by studying its stability against linear gravitational and matter perturbations, fixing $\omega_V$ 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., Comment: 13 pages and 4 figures

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., Comment: 23 pages, 4 figures

In this paper we study a modified version of unimodular general relativity in the context of $f(G)$, $G$ denoting the Gauss-Bonnet invariant. We attach attention to Bianchi-type I and Friendmann-Robertson-Walker universes and search for unimodular $f(G)$ models according to the de Sitter and power-law solutions. Assuming unimodular $f(G)$ gravity as perfect fluid and making use of the slow-roll parameters, inflationary model has been reconstructed in concordance with the Planck observational data. Moreover, we investigate the realization of the bounce and loop quantum cosmological ekpyrotic paradigms. Assuming suitable and appropriated scale factors, unimodular $f(G)$ models able to reproduce superbounce and ekpyrotic scenarios have been reconstructed., Comment: 14 pages

In this paper, we investigate the late-time cosmic acceleration in mimetic $f(R,T)$ gravity with Lagrange multiplier and potential in a Universe containing, besides radiation and dark energy, a self-interacting (collisional) matter. We obtain through the modified Friedmann equations, the main equation that can describe the cosmological evolution and with several models from $Q(z)$ and the well known particular model $f(R, T)$, we perform an analysis of the late-time evolution. We examine the behavior of the Hubble parameter, the dark energy equation of state and the total effective equation of state and we compare in each case the resulting picture with the non-collisional matter (assumed as dust) and also with the collisional matter in mimetic $f(R, T)$ gravity. The results obtained are in good agreement with the observational data and show that in presence of the collisional matter the dark energy oscillations in mimetic f(R, T) gravity can be damped., Comment: 18 pages, 2 figures

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., Comment: 23 pages and 5 figures. arXiv admin note: text overlap with arXiv:1212.5774 by other authors

We examine in this paper the stability analysis in $f(R; T; R_{\mu\nu}T^{\mu\nu})$ 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 $f(R; T; R_{\mu\nu}T^{\mu\nu})$ model by solving numerically the perturbation functions obtained., Comment: 16 pages, 2 figures

In this paper, we study in Friedmann-Robertson-Walker universe the interaction between the viscous generalized Chaplygin gas with $f(R,T)$ gravity, which is an arbitrary function of the Ricci scalar $R$ and the trace $T$ of the energy-momentum tensor. Assuming that the contents of universe is dominated by a generalized Chaplygin gas and dark energy, we obtained the modified Friedmann equations and also the time dependent energy density and pressure of dark energy due to the shear and bulk viscosities for three interacting models depending on an input parameter $Q$. Within the simple form of scale factor (power-law), we discuss the graphical representation of dark energy density parameter and investigate the shear and bulk viscosities effects on the accelerating expansion of the universe for each interacting model., Comment: 10 pages and 5 figures

The Geodesic Deviation Equation is being studied in Brans-Dicke-Rastall gravity. We briefly discuss the Brans-Dicke-Rastall gravity and then construct GDE for FLRW metric. In this way, the obtained geodesic deviation equation will correspond to the Brans-Dicke-Rastall gravity. Eventually, we solve numerically the null vector GDE to obtain from Mattig relation, the deviation vector $\eta(z)$ and observer area distance $r_0(z)$ and compare the results with $\Lambda$CDM model., Comment: 20 pages, 4 figures

We have studied in this paper, the stability of dynamical system in $f(R)$ gravity. We have considered the $f(R)$ $\gamma$-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., Comment: 16 pages and 6 figures, version accepted for publication in IJMPD

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 $\tau$. 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 $\Lambda$, Comment: 11 pages

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., Comment: 14 pages and 7 figures

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 $T=T_{\mu}^{\mu}$. This type of modified gravity is called as $f(R,T)$ in which $R$ is Ricci scalar $R=R_{\mu}^{\mu}$. 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., Comment: 14 pages, revtex4 format. arXiv admin note: text overlap with arXiv:1104.2669 by other authors

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., Comment: 20 pages, 2 figures

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., Comment: 23 pages, 16 figures

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., Comment: 16 pages and 4 figures

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.

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.

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., Comment: 18 pages. Accepted for publication in Astrophys Space Science. arXiv admin note: text overlap with arXiv:1410.3993 by other authors

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., Comment: 23 pages

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 $\Lambda$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., Comment: 17 pages and 8 figues

We have been studied the model of light Galileon with translational shift symmetry $\phi\to \phi+c$. The matter Lagrangian is presented in the form $\mathcal{L}_{\phi}= -\eta (\partial \phi)^2+\beta G^{\mu\nu}\partial_{\mu}\phi\partial_{\nu}\phi$. 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 $f(R,R^{\mu\nu}T_{\mu\nu}^m)$. 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 $\phi=t$, which it is remembered by us dilaton field., Comment: Accepted in "International Journal of Theoretical Physics"

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., Comment: 19 pages, 3 figures

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., Comment: 15 pages, 4 figues

We study the locally rotational symmetry Bianchi type-I dark energy model in the framework of $f(T)$ theory of gravity, where $T$ denotes the torsion scalar. A viable cosmological model is undertaken and the isotropization of this latter is checked, yielding a result that reflects the real evolution of our universe. Moreover, still in the anisotropic optic, a more complicated $f(T)$ model is obtained from the cosmological reconstruction scheme and the analysis shows that the universe is more anisotropic at the beginning if the terms of higher order in $T$ are not considered. This means that the non-linear model should be favoured by observational data., Comment: 20 pages, 10 figures, Accepted for publication in International Journal of Modern Physics D (IJMPD)

In the present paper we study warm inflationary universe models in the context of a polytropic gas. We derive the characteristics of this model in slow-roll approximation and develop our model in two cases, 1- For a constant dissipative parameter $\Gamma$. 2- $\Gamma$ as a function of scalar field $\phi$. In these cases we will obtain exact solution for the scalar field and Hubble parameter. We will also obtain explicit expressions for the tensor-scalar ratio $R$, scalar spectrum index $n_s$ and its running $\alpha_s$, in slow-roll approximation., Comment: 13 pages, 1 figure

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., Comment: 25 pages, 2 figures, Accepted for publication in Journal of Cosmology and Astroparticle Physics (JCAP)

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., Comment: 16 pages, 3 figure, version accepted for publication in Journal of Cosmology and Astroparticle Physics (JCAP)

We formulate evaporation phenomena in a generic model of generalized teleparallel gravity in Weitzenbock spacetime with diagonal and non-diagonal tetrads basis. We also perform the perturbation analysis around the constant torsion scalar solution named Nariai spacetime which is an exact solution of field equations as the limiting case of the Schwarzschild-de Sitter and in the limit where two back hole and their cosmological horizons coincide. By a carefully analysis of the horizon perturbation equation, we show that (anti)evaporation can not happen if we use a diagonal tetrad basis. This result implies that a typical black hole in any generic form of generalized teleparallel gravity is frozen in its initial state if we use the diagonal tetrads. But in the case of non-diagonal tetrads the analysis is completely different. By a suitable non trivial non-diagonal tetrad basis we investigate the linear stability of the model under perturbations of the metric and torsion simultaneously. We observe that in spite of the diagonal case, both evaporation and anti evaporation can happen. The phenomena depend on the initial phase of the horizon perturbation. In the first mode when we restrict ourselves to the first lower modes the (anti)evaporation happens. So, in non-diagonal case the physical phenomena is reasonable. This is an important advantage of using non-diagonal tetrads instead of the diagonal ones. We also see that this is an universal feature, completely independent from the form of the model., Comment: 16 pages, 2 figures

Exact solutions for planar Weitzenboch geometries in generalized teleparallel gravity with torsion is presented. The model predicted the existence of Moller, Kattler-Wittaker and planar de-Sitter geometries for different forms of action., Comment: 17 pages, Accepted for publication International Journal of Modern Physics D (IJMPD)

In the context of f(R,T) theories of gravity, we study the evolution of scalar cosmological perturbations in the metric formalism. According to restrictions on the background evolution, a specific model within these theories is assumed in order to guarantee the standard continuity equation. Using a completely general procedure, we find the complete set of differential equations for the matter density perturbations. In the case of sub-Hubble modes, the density contrast evolution reduces to a second-order equation. We show that for well-motivated f(R,T) Lagrangians the quasistatic approximation yields to very different results from the ones derived in the frame of the concordance {\Lambda}CDM model constraining severely the viability of such theories., Comment: 11 pages, 3 figures, revtex4 format, minor changes to match version as published version, published version in PRD

We present cylindrically symmetric solutions for a type of the Gauss-Bonnet gravity, in details. We derive the full system of the field equations and show that there exist seven families of exact solutions for three forms of viable models. By applying the method based on the effective fluid energy momentum tensor components, we evaluate the mass per unit length for the solutions. From dynamical point of the view, by evaluating the null energy condition for these configurations, we show that in some cases the azimuthal pressure breaks the energy condition. This violation of the null energy condition predicts the existence of a cylindrical wormhole., Comment: 27 pages

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., Comment: 5 pages, revtex4 format, Accepted for publication in CJP

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., Comment: 16 pages, 4 figures. arXiv admin note: text overlap with arXiv:1011.6255 by other authors

We investigate the cosmological reconstruction in anisotropic universe for both homogeneous and inhomogeneous content of the universe. Special attention is attached to three interesting cases: Bianchi type-I, Bianchi type-III and Kantowski-Sachs models. The de Sitter, power-law and general exponential solutions are assumed for the scale factor in each spatial direction and the corresponding cosmological models are reconstructed. Moreover, for the general exponential solutions, from which the de Sitter and power-law solutions may be obtained, we obtain models which reproduce the early universe, assumed as the inflation, and the late time accelerated expanding universe. The models obtained for the late time universe are consistent with a known result in literature where a power-law type correction in T is added to a power-law type of f(T) for guaranteeing the avoidance of the Big Rip and the Big Freeze., Comment: 16 pages, revtex4 format, version accepted for publication in Physical Review D

Cosmological reconstruction of Little Rip model in $f(R, T)$ gravity is investigated, where $R$ is the curvature scalar and $T$ the trace of the energy momentum tensor. The model perfectly reproduces the present stage of the universe, characterized by the $\Lambda CDM$ model, without singularity at future finite-time (without the Big Rip). The input parameters are determined according to Supernovae Cosmology data and perfectly fit with the WMAP around the Little Rip. Moreover, the thermodynamics is considered in this Little Rip cosmology and it is illustrated that the second law of thermodynamics is always satisfied around the Little Rip universe for the temperature inside the horizon being the same as that of the apparent horizon. Moreover, we show the existence of a stable fixed point in the Little Rip universe which confirms that this is actually a late-time attractor in the phantom-dominated universe. The linear perturbation analysis is performed around the critical points, showing that the Little Rip model obtained is stable., Comment: 18 pages

We investigate static cylindrically symmetric vacuum solutions in Weyl coordinates in the framework of f(T) theories of gravity, where T is the torsion scalar. The set of modified Einstein equations is presented and the fourth coming equations are established. Specific physical expressions are assumed for the algebraic function f(T) and solutions are obtained. Moreover, general solution is obtained with finite values of u(r) on the axis r = 0, and this leads to a constant torsion scalar. Also, cosmological constant is introduced and its relation to Linet-Tian solution in GR is commented., Comment: 13 pages; Accepted for publication in International Journal of Modern Physics D (IJMPD)