TIME-DEPENDENT WORMHOLE SOLUTIONS OF f(R) THEORY OF GRAVITY AND ENERGY CONDITIONS (original) (raw)
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In this work wormholes in viable f(R) gravity models are analysed. We are interested in exact solutions for stress-energy tensor components depending on different shape and redshift functions. Several solutions of gravitational equations for different f(R) models are examined. Found solutions imply no need for exotic material, while this need is implied in the standard general theory of relativity. A simple expression for WEC violation near the throat is derived and analysed. High curvature regime is also discussed, as well as the question of the highest possible values of the Ricci scalar for which the WEC is not violated near the throat, and corresponding functions are calculated for several models. The approach here differs from the one that has been common since no additional assumptions to simplify the equations have been made, and functions in f(R) models are not considered to be arbitrary functions, but rather a feature of the theory that has to be evaluated on the basis of c...
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Traversable wormhole solutions in General Relativity require exotic matter sources that violate the null energy condition (NEC), and such behavior may be avoided in modified gravity. In this study, we analyze the energy conditions for static, spherically symmetric traversable Morris–Thorne wormholes in a recently proposed viable [Formula: see text] gravity model. We numerically analyze solutions considering both constant and variable redshift functions, and present wormhole spacetimes respecting the NEC, supported by a phantom energy-like equation of state for the source. Moreover, we analyze the stability of the spacetimes using the generalized Tolman–Oppenheimer–Volkov equation. We demonstrate the effects of certain parameters in the [Formula: see text] model in determining energy condition violations, and establish that stable wormholes can be formulated only at the expense of violating the NEC.
Wormholes in viable f(R)$$ f ( R ) modified theories of gravity and weak energy condition
The European Physical Journal C, 2015
In this work wormholes in viable f (R) gravity models are analyzed. We are interested in exact solutions for stress-energy tensor components depending on different shape and redshift functions. Several solutions of gravitational equations for different f (R) models are examined. The solutions found imply no need for exotic material, while this need is implied in the standard general theory of relativity. A simple expression for weak energy condition (WEC) violation near the throat is derived and analyzed. High curvature regime is also discussed, as well as the question of the highest possible values of the Ricci scalar for which the WEC is not violated near the throat, and corresponding functions are calculated for several models. The approach here differs from the one that has been common since no additional assumptions to simplify the equations have been made, and the functions in f (R) models are not considered to be arbitrary functions, but rather a feature of the theory that has to be evaluated on the basis of consistency with observations for the Solar System and cosmological evolution. Therefore in this work we show that the existence of wormholes without exotic matter is not only possible in simple arbitrary f (R) models, but also in models that are in accordance with empirical data.
Advances in Astronomy, 2021
In Einstein’s relativity theory, the existence of traversable wormholes requires the involvement of exotic matter which violates the null energy condition (NEC). Our aim, in this article, is to construct wormhole solutions with the nonexotic matter. To achieve this, we choose an interesting gravitational framework of f ℛ , T theory which contains a quadratic term of energy-momentum tensor T i j trace and a well-known Starobinsky f ℛ model in its extended form. We analyze the behavior of energy constraints in the framework of f ℛ , T = ℛ + α ℛ 2 + γ ℛ n + λ T 2 (where α , γ , and λ are some random constants) model for the well-proposed shape function S r = r 0 r 0 / r ε (where ε is a constant and r 0 is the wormhole throat). A detailed analysis of validity regions is presented for some choices of coupling parameters along with the free parameter of EoS β , m . It is shown that, under this model, the existence of viable wormhole geometry is possible without requiring any exotic matter.
Wormhole geometries in f(R) modified theories of gravity
Physical Review D, 2009
In this work, we construct traversable wormhole geometries in the context of f (R) modified theories of gravity. We impose that the matter threading the wormhole satisfies the energy conditions, so that it is the effective stress-energy tensor containing higher order curvature derivatives that is responsible for the null energy condition violation. Thus, the higher order curvature terms, interpreted as a gravitational fluid, sustain these non-standard wormhole geometries, fundamentally different from their counterparts in general relativity. In particular, by considering specific shape functions and several equations of state, exact solutions for f (R) are found.
Traversable wormholes in the traceless f(R,T) gravity
International Journal of Modern Physics D
Wormholes are tunnels connecting different regions in spacetime. They were obtained originally as a solution for Einstein’s General Theory of Relativity and according to this theory they need to be filled by an exotic kind of anisotropic matter. In the present sense, by “exotic matter” we mean matter that does not satisfy the energy conditions. In this paper, we propose the modeling of traversable wormholes (i.e. wormholes that can be safely crossed) within an alternative gravity theory that proposes an extra material (rather than geometrical) term in its gravitational action, namely the traceless [Formula: see text] theory of gravitation, with [Formula: see text] and [Formula: see text] being, respectively, the Ricci scalar and trace of the energy–momentum tensor. Our solutions are obtained from well-known particular cases of the wormhole metric potentials, namely redshift and shape functions. In possession of the solutions for the wormhole material content, we also apply the energ...
Wormholes in f(R,T)f(R,T)f(R,T) gravity satisfying the null energy condition with isotropic pressure
arXiv (Cornell University), 2020
We consider the f (R, T) theory of gravity, in which the gravitational Lagrangian is given by an arbitrary function of the Ricci scalar and the trace of the energy-momentum tensor, to study static spherically symmetric wormhole geometries sustained by matter sources with isotropic pressure. According to restrictions on the wormhole geometries, we carefully adopt different strategies to construct solutions with the properties and characteristics of wormholes. Using an utterly general procedure, we provide several examples of wormholes in which the matter threading the wormhole throat satisfies all of the energy conditions and discuss general mechanisms for finding them. Finally, we postulate a smooth transformation for simplifying the nonlinear field equations and have more consistent results than the other ones to conclude that the results can be viewed as specific exact wormhole solutions without exotic matter.
Necessary conditions for having wormholes in f(R) gravity
Modern Physics Letters A
For a generic f(R) which admits a polynomial expansion, we find the near-throat wormhole solution. Necessary conditions for the existence of wormholes in such f(R) theories are derived for both zero and nonzero matter sources. For vanishing external sources, we show that the energy conditions are violated. A particular choice of energy–momentum reveals that the wormhole geometry satisfies the weak energy condition (WEC). For a range of parameters, even the strong energy condition (SEC) is shown to be satisfied.
Wormholes in a viable f (T) gravity
2013
In this paper, we derive some new exact solutions of static wormholes in f (T ) gravity. We discuss independent cases of the pressure components including isotropic and anisotropic pressure. Lastly we consider radial pressure satisfying a barotropic equation of state. We also check the behavior of null energy condition (NEC) for each case and observe that it is violated for anisotropic while it is satisfied for isotropic and barotropic cases.
Study of static wormhole solutions in F(T,TG) gravity
Annals of Physics
In this paper, we investigate static spherically symmetric wormhole solutions in the background of F (T, T G) gravity (T is the torsion scalar and T G represents teleparallel equivalent of the Gauss-Bonnet term). We study the wormhole solutions by assuming four different matter contents, a specific redshift function and a particular F (T, T G) model. The behavior of null/weak energy conditions for these fluids is analyzed graphically. It turns out that wormhole solutions can be obtained in the absence of exotic matter for some particular regions of spacetime. We also explore stability of wormhole solutions through equilibrium condition. It is concluded that there exist physically acceptable wormhole solutions for anisotropic, isotropic and traceless fluids.