Exact wormholes solutions without exotic matter in f(R,T) gravity

2019 ◽  
Vol 16 (03) ◽  
pp. 1950046 ◽  
Author(s):  
M. Zubair ◽  
Rabia Saleem ◽  
Yasir Ahmad ◽  
G. Abbas
Keyword(s):  
Momentum Tensor ◽  
Exotic Matter ◽  
Gravity Models ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Energy Tensor ◽  
Field Equations ◽  
Stress Energy ◽  
Symmetric Geometry ◽  
The Stability

This paper is aimed to evaluate the existence of wormholes in viable [Formula: see text] gravity models (where [Formula: see text] is the scalar curvature and [Formula: see text] is the trace of stress–energy tensor of matter). The exact solutions for energy–momentum tensor components depending on different shapes and redshift functions are calculated without some additional constraints. To investigate this, we consider static spherically symmetric geometry with matter contents as anisotropic fluid and formulate the Einstein field equations for three different [Formula: see text] models. For each model, we derive expression for weak and null energy conditions and graphically analyzed its violation near the throat. It is really interesting that wormhole solutions do not require the presence of exotic matter — like that in general relativity. Finally, the stability of the solutions for each model is presented using equilibrium condition.

Power law f(𝒢,T) gravity models supporting wormhole solutions

2018 ◽  
Vol 15 (05) ◽  
pp. 1850070 ◽  
Author(s):  
M. Farasat Shamir ◽  
Mushtaq Ahmad
Keyword(s):  
Power Law ◽  
Momentum Tensor ◽  
Matter Content ◽  
Gravity Models ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Ordinary Matter ◽  
Specific Formula ◽  
The Stability ◽  
Modified Formula

This work provides some feasible regions for the existence of traversable wormhole geometries in modified [Formula: see text] gravity. For this purpose, three different matter contents have been studied with special emphasis on anisotropic fluid by considering a specific [Formula: see text] gravity power law model. It has been shown that the null energy conditions for the effective energy–momentum tensor are widely violated for the ordinary matter content. However, some small feasible regions to support the wormhole solutions have been noted. Furthermore, the stability of the anisotropic feasible regions for the wormhole solutions has been discussed. It is concluded that the wormhole geometries threaded by the ordinary matter actually exist and are well stable in [Formula: see text] gravity.

scholarly journals Stability of the Regular Hayward Thin-Shell Wormholes

2016 ◽  
Vol 2016 ◽  
pp. 1-13 ◽  
Author(s):  
M. Sharif ◽  
Saadia Mumtaz
Keyword(s):  
Black Hole ◽  
Thin Shell ◽  
Energy Conditions ◽  
Stability Conditions ◽  
Energy Tensor ◽  
Stress Energy Tensor ◽  
Cosmic Expansion ◽  
Stress Energy ◽  
Thin Shell Wormholes ◽  
The Stability

The aim of this paper is to construct regular Hayward thin-shell wormholes and analyze their stability. We adopt Israel formalism to calculate surface stresses of the shell and check the null and weak energy conditions for the constructed wormholes. It is found that the stress-energy tensor components violate the null and weak energy conditions leading to the presence of exotic matter at the throat. We analyze the attractive and repulsive characteristics of wormholes corresponding toar>0andar<0, respectively. We also explore stability conditions for the existence of traversable thin-shell wormholes with arbitrarily small amount of fluid describing cosmic expansion. We find that the space-time has nonphysical regions which give rise to event horizon for0<a0<2.8and the wormhole becomes nontraversable producing a black hole. The nonphysical region in the wormhole configuration decreases gradually and vanishes for the Hayward parameterl=0.9. It is concluded that the Hayward and Van der Waals quintessence parameters increase the stability of thin-shell wormholes.

Study of gravitational decoupled anisotropic solution

2019 ◽  
Vol 28 (16) ◽  
pp. 2040004
Author(s):  
M. Sharif ◽  
Sobia Sadiq
Keyword(s):  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Spherically Symmetric ◽  
Anisotropic Model ◽  
Field Equations ◽  
Anisotropic Solution ◽  
Spherically Symmetric Solution ◽  
Gravitational Source ◽  
The Stability

This paper formulates the exact static anisotropic spherically symmetric solution of the field equations through gravitational decoupling. To accomplish this work, we add a new gravitational source in the energy–momentum tensor of a perfect fluid. The corresponding field equations, hydrostatic equilibrium equation as well as matching conditions are evaluated. We obtain the anisotropic model by extending the known Durgapal and Gehlot isotropic solution and examined the physical viability as well as the stability of the developed model. It is found that the system exhibits viable behavior for all fluid variables as well as energy conditions and the stability criterion is fulfilled.

scholarly journals Schwarzschild-de Sitter and Anti-de Sitter Thin-Shell Wormholes and Their Stability

2014 ◽  
Vol 2014 ◽  
pp. 1-13 ◽  
Author(s):  
M. Sharif ◽  
Saadia Mumtaz
Keyword(s):  
Thin Shell ◽  
Chaplygin Gas ◽  
Exotic Matter ◽  
Energy Conditions ◽  
Energy Tensor ◽  
De Sitter ◽  
Stress Energy ◽  
Linear Perturbations ◽  
Unstable Solutions ◽  
Thin Shell Wormholes

This paper is devoted to construct Schwarzschild-de Sitter and anti-de Sitter thin-shell wormholes by employing Visser’s cut and paste technique. The Darmois-Israel formalism is adopted to formulate the surface stresses of the shell. We analyze null and weak energy conditions as well as attractive and repulsive characteristics of thin-shell wormholes. We also explore stable and unstable solutions against linear perturbations by taking two different Chaplygin gas models for exotic matter. It is concluded that the stress-energy tensor components violate the null and weak energy conditions indicating the existence of exotic matter at the wormhole throat. Finally, we find unstable and stable configurations for the constructed thin-shell wormholes.

scholarly journals Constructions of f(R,G,𝒯) gravity from some expansions of the Universe

2020 ◽  
Vol 35 (31) ◽  
pp. 2050203
Author(s):  
Ujjal Debnath
Keyword(s):  
Energy Conditions ◽  
Energy Tensor ◽  
De Sitter ◽  
Field Equations ◽  
Least Action Principle ◽  
Future Singularity ◽  
Least Action ◽  
The Least Action Principle ◽  
Modified Gravity Theory ◽  
Stress Energy

Here we propose the extended modified gravity theory named [Formula: see text] gravity where [Formula: see text] is the Ricci scalar, [Formula: see text] is the Gauss–Bonnet invariant, and [Formula: see text] is the trace of the stress-energy tensor. We derive the gravitational field equations in [Formula: see text] gravity by taking the least action principle. Next we construct the [Formula: see text] in terms of [Formula: see text], [Formula: see text] and [Formula: see text] in de Sitter as well as power-law expansion. We also construct [Formula: see text] if the expansion follows the finite-time future singularity (big rip singularity). We investigate the energy conditions in this modified theory of gravity and examine the validity of all energy conditions.

scholarly journals General approach to the Lagrangian ambiguity in f(R, T) gravity

2021 ◽  
Vol 81 (2) ◽  
Author(s):  
G. A. Carvalho ◽  
F. Rocha ◽  
H. O. Oliveira ◽  
R. V. Lobato
Keyword(s):  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Modified Theories Of Gravity ◽  
Energy Tensor ◽  
Field Equations ◽  
Unknown Variable ◽  
Stress Energy ◽  
The Standard Model ◽  
Theories Of Gravity ◽  
Matter Fields

AbstractThe f(R, T) gravity is a theory whose gravitational action depends arbitrarily on the Ricci scalar, R, and the trace of the stress–energy tensor, T; its field equations also depend on matter Lagrangian, $$\mathscr {L}_{m}$$ L m . In the modified theories of gravity where field equations depend on Lagrangian, there is no uniqueness on the Lagrangian definition and the dynamics of the gravitational and matter fields can be different depending on the choice performed. In this work, we have eliminated the $$\mathscr {L}_{m}$$ L m dependence from f(R, T) gravity field equations by generalizing the approach of Moraes in Ref. [1]. We also propose a general approach where we argue that the trace of the energy–momentum tensor must be considered an “unknown” variable of the field equations. The trace can only depend on fundamental constants and few inputs from the standard model. Our proposal resolves two limitations: first the energy–momentum tensor of the f(R, T) gravity is not the perfect fluid one; second, the Lagrangian is not well-defined. As a test of our approach we applied it to the study of the matter era in cosmology, and the theory can successfully describe a transition between a decelerated Universe to an accelerated one without the need for dark energy.

Non-adiabatic gravitational collapse in f(R,T) gravity with Karmarkar condition for anisotropic fluid

2020 ◽  
Vol 35 (13) ◽  
pp. 2050103 ◽  
Author(s):  
Riaz Ahmed ◽  
G. Abbas
Keyword(s):  
Gravitational Collapse ◽  
Coupling Parameter ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Interior Solution ◽  
Spatial Presence ◽  
Field Equations ◽  
Gravitational Field Equations ◽  
Radiating Star

In this paper, we have used the Karmarkar condition to the spherically symmetric non-static radiating star experiencing dissipative gravitational collapse with a heat flux in the framework of [Formula: see text] gravity, (where [Formula: see text] is Ricci scalar which replaces Lagrangian density and [Formula: see text] is the trace of energy–momentum tensor). To obtain the ultimate results of the gravitational field equations in [Formula: see text] scenario, we take a linear form of the function as [Formula: see text]. In this connection, the Karmarkar condition along with boundary condition generates a model of radiating star and enables us to completely indicate the spatial presence of gravitational potentials. Vadiya’s exterior solution across a time-like hypersurface is smoothly matched to the interior solution which allows to study the physical conduct of our model under consideration. Furthermore, we have analyzed the energy conditions of radiating star in [Formula: see text] gravity and analyzed the physical behavior of thermodynamics parameters which provide a detailed discussion of the model. For coupling parameter [Formula: see text], we successfully obtain the standard results of General Relativity.

Stability of anisotropic perturbed Einstein universe in f(R,T) theory

2020 ◽  
Vol 35 (27) ◽  
pp. 2050222
Author(s):  
M. Sharif ◽  
Sana Saleem
Keyword(s):  
General Relativity ◽  
State Parameter ◽  
Fluid Distribution ◽  
Energy Tensor ◽  
Stress Energy Tensor ◽  
Field Equations ◽  
Scale Factors ◽  
Stress Energy ◽  
Equation Of State Parameter ◽  
The Stability

The aim of this paper is to investigate the stability of Einstein static cosmos using anisotropic homogeneous perturbations in the background of [Formula: see text] theory in which [Formula: see text] and [Formula: see text] express the Ricci scalar and trace of the stress–energy tensor, respectively. To accomplish this work, we consider perfect fluid distribution and adopt small anisotropic perturbations in the scale factors and matter contents. We develop static and perturbed field equations that are simplified by using equation of state parameter. For the specific models of [Formula: see text] theory with conserved and non-conserved stress–energy tensor, the Einstein solutions are explored and their stability regions are analyzed graphically. We conclude that the static Einstein stable universe with anisotropic perturbations exists in this framework contrary to general relativity.

scholarly journals Energy condition in unimodular f(R, T) gravity

2021 ◽  
Vol 81 (3) ◽  
Author(s):  
Fateme Rajabi ◽  
Kourosh Nozari
Keyword(s):  
Power Law ◽  
Energy Condition ◽  
Energy Conditions ◽  
Energy Tensor ◽  
De Sitter ◽  
Stress Energy Tensor ◽  
Modified Gravity Theory ◽  
Stress Energy ◽  
The Stability ◽  
Interesting Alternative

AbstractWe study an interesting alternative of modified gravity theory, namely, the unimodular f(R, T) gravity in which R is the Ricci scalar and T is the trace of the stress–energy tensor. We study the viability of the model by using the energy conditions. We discuss the strong, weak, null and dominant energy conditions in terms of deceleration, jerk and snap parameters. We investigate energy conditions for reconstructed unimodular f(R, T) models and give some constraints on the parametric space of the model. We observe that by setting appropriately free parameters, energy conditions can be satisfied. Furthermore, we study the stability of the solutions in perturbations framework. In this case, we investigate stability conditions for de Sitter and power law solutions and we examine viability of cosmological evolution of these perturbations. The results show that for some values of the input parameters, for which energy conditions are satisfied, de Sitter and power-law solutions may be stable.

scholarly journals Cylindrically Symmetric, Asymptotically Flat, Petrov Type D Spacetime with a Naked Curvature Singularity and Matter Collapse

2017 ◽  
Vol 2017 ◽  
pp. 1-6 ◽  
Author(s):  
Faizuddin Ahmed
Keyword(s):  
Cosmic Time ◽  
Petrov Type ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Curvature Singularity ◽  
Field Equations ◽  
Asymptotically Flat ◽  
Type D ◽  
Cylindrically Symmetric ◽  
Petrov Type D

We present a cylindrically symmetric, Petrov type D, nonexpanding, shear-free, and vorticity-free solution of Einstein’s field equations. The spacetime is asymptotically flat radially and regular everywhere except on the symmetry axis where it possesses a naked curvature singularity. The energy-momentum tensor of the spacetime is that for an anisotropic fluid which satisfies the different energy conditions. This spacetime is used to generate a rotating spacetime which admits closed timelike curves and may represent a Cosmic Time Machine.

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