scholarly journals Phantom fluid wormhole in f(R, T) gravity

2019 ◽  
Vol 34 (37) ◽  
pp. 1950303 ◽  
Author(s):  
Parbati Sahoo ◽  
Annika Kirschner ◽  
P. K. Sahoo
Keyword(s):  
Modified Gravity ◽  
Energy Condition ◽  
Phantom Energy ◽  
Null Energy Condition ◽  
Energy Conditions ◽  
Spherically Symmetric ◽  
Phantom Dark Energy ◽  
Modified Gravity Theories ◽  
De Formula ◽  
Modified Formula

Wormholes (WHs) are considered as hypothetical shortcuts or tunnels in spacetime. In general relativity (GR), the fundamental ingredient of WH geometry is the presence of exotic matter at the throat, which is responsible for the violation of null energy condition (NEC). However, the modified gravity theories have shown to be able to provide WH solutions satisfying energy conditions (ECs). In this paper, we study the static spherically symmetric WH solutions in modified [Formula: see text] gravity for a phantom fluid case. The exact solutions of this model are obtained through the equation of state (EoS), [Formula: see text], associated with phantom dark energy (DE) [Formula: see text]. We find the existence of spherically symmetric WH solution supported by phantom energy distribution. The shape function of the WH obtained in this model obeys all the WH metric conditions. In modified gravity scenario, the phantom fluid WH violates the NEC in radial case, unlike in the tangential case. Furthermore, using the “volume integral quantifier” (VIQ) method, the total amount of EC violating matter in spacetime is discussed briefly.

Wormhole structures and energy conditions in f(ℛ) gravity with hybrid shape functions

2021 ◽  
pp. 2150065
Author(s):  
Ouziala Ikram ◽  
Mushtaq Ahmad ◽  
G. Mustafa
Keyword(s):  
Energy Condition ◽  
Null Energy Condition ◽  
Graphical Analysis ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Collective Effects ◽  
Shape Functions ◽  
Energy Constraints ◽  
Modified Formula ◽  
Two Hybrid

This paper discusses the possible wormhole solutions in modified [Formula: see text] gravity by employing the two hybrid shape functions i.e. [Formula: see text] and [Formula: see text], where [Formula: see text] is constant. The solutions are accomplished by implementing the modified-gravity functions [Formula: see text] and [Formula: see text], where [Formula: see text]. It is presented by investigating the energy constraints through the graphical analysis that the null energy conditions for the energy–momentum tensor are largely violated for our both models. Energy constraints connected to the matter source threading the possible wormhole structures are in general worked out, supporting the null energy constraints in the neighborhood of the wormhole neck. This concludes that threaded by the matter, the existence of the non-exotic wormhole geometries have been found in this gravity. Subsequently, it is shown that violation of the null energy condition may be accredited to the collective effects of the [Formula: see text] gravity and owing to the non-commutative geometry.

A study of some cylindrically symmetric solutions in f(R, G) gravity

2020 ◽  
Vol 98 (4) ◽  
pp. 364-374
Author(s):  
Saeeda Zia ◽  
M. Farasat Shamir
Keyword(s):  
Exact Solutions ◽  
Modified Gravity ◽  
Complete System ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Energy Conditions ◽  
Model Parameters ◽  
Field Equations ◽  
Cylindrically Symmetric ◽  
Modified Theory

In this paper, we present the cylindrically symmetric solutions in a well-known modified theory, namely f(R, G) gravity. After driving the complete system of field equations, six different families of exact solutions using a viable f(R, G) gravity model have been discussed. Moreover, we have investigated the well-known Levi–Civita solution in modified gravity for the model f(R, G) = R2 + αGn for some suitable values of model parameters n and α. Null energy conditions are also calculated for all the obtained solutions. Some regions are observed where the null energy condition is violated, indicating the existence of cylindrical wormholes.

scholarly journals Wormhole geometries in f(Q) gravity and the energy conditions

2021 ◽  
Vol 81 (11) ◽  
Author(s):  
Ayan Banerjee ◽  
Anirudh Pradhan ◽  
Takol Tangphati ◽  
Farook Rahaman
Keyword(s):  
Energy Condition ◽  
Null Energy Condition ◽  
Specific Form ◽  
Energy Conditions ◽  
Recent Theory ◽  
Spherically Symmetric ◽  
Shape Functions ◽  
Field Equations ◽  
Form Function

AbstractFollowing the recent theory of f(Q) gravity, we continue to investigate the possible existence of wormhole geometries, where Q is the non-metricity scalar. Recently, the non-metricity scalar and the corresponding field equations have been studied for some spherically symmetric configurations in Mustafa (Phys Lett B 821:136612, 2021) and Lin and Zhai (Phys Rev D 103:124001, 2021). One can note that field equations are different in these two studies. Following Lin and Zhai (2021), we systematically study the field equations for wormhole solutions and found the violation of null energy conditions in the throat neighborhood. More specifically, considering specific choices for the f(Q) form and for constant redshift with different shape functions, we present a class of solutions for static and spherically symmetric wormholes. Our survey indicates that wormhole solutions could not exist for specific form function $$f(Q)= Q+ \alpha Q^2$$ f ( Q ) = Q + α Q 2 . To summarize, exact wormhole models can be constructed with violation of the null energy condition throughout the spacetime while being $$\rho \ge 0$$ ρ ≥ 0 and vice versa.

Formation of wormholes in modified gravity: Exotic matter and stability

2019 ◽  
Vol 34 (25) ◽  
pp. 1950200
Author(s):  
Subhra Bhattacharya ◽  
Shibaji Halder ◽  
Subenoy Chakraborty
Keyword(s):  
Modified Gravity ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Einstein Gravity ◽  
Einstein Equations ◽  
Exotic Matter ◽  
Field Equations ◽  
Normal Fluid ◽  
Modified Gravity Theories ◽  
Gravity Theories

This work addresses the question whether exotic matter is essential for the formation of wormholes in modified gravity theories. The basic property of wormhole geometry is the flaring-out condition at the throat which essentially states the violation of null energy condition for the matter threading the wormhole in Einstein gravity. In modified gravity theories, the field equations can be written as Einstein equations with two non-interacting fluids of which one is the usual fluid under consideration and the second term, called the effective matter, comes from the extra geometric terms of the theory. So it is interesting to examine whether normal fluid with restrictions on geometry satisfies the conditions for the formation of wormholes and their stability.

scholarly journals BEHAVIOR OF TACHYON IN STRING COSMOLOGY BASED ON GAUGED WZW MODEL

2009 ◽  
Vol 24 (04) ◽  
pp. 277-289
Author(s):  
SUNGGEUN LEE ◽  
SOONKEON NAM
Keyword(s):  
Cosmological Model ◽  
Energy Condition ◽  
Flat Space ◽  
Null Energy Condition ◽  
Energy Conditions ◽  
Dilaton Field ◽  
Coset Space ◽  
Tachyon Field ◽  
Strong Energy ◽  
Matter Fields

We investigate a string theoretic cosmological model in the context of the gauged Wess–Zumino–Witten model. Our model is based on a product of non-compact coset space and a spectator flat space; [ SL (2, R)/ U (1)]k × ℝ2. We extend the formerly studied semiclassical consideration with infinite Kac–Moody level k to a finite one. In this case, the tachyon field appears in the effective action, and we solve the Einstein equation to determine the behavior of tachyon as a function of time. We find that tachyon field dominates over dilaton field in early times. In particular, we consider the energy conditions of the matter fields consisting of the dilaton and the tachyon which affect the initial singularity. We find that not only the strong energy but also the null energy condition is violated.

scholarly journals Dark Matter Candidates with Dark Energy Interiors Determined by Energy Conditions

Symmetry ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 662 ◽  
Author(s):  
Irina Dymnikova
Keyword(s):  
Dark Matter ◽  
Dark Energy ◽  
Energy Condition ◽  
Phantom Energy ◽  
Weak Energy Condition ◽  
Energy Conditions ◽  
De Sitter ◽  
Dynamical Equations ◽  
De Sitter Vacuum ◽  
Observational Signature

We outline the basic properties of regular black holes, their remnants and self-gravitating solitons G-lumps with the de Sitter and phantom interiors, which can be considered as heavy dark matter (DM) candidates generically related to a dark energy (DE). They are specified by the condition T t t = T r r and described by regular solutions of the Kerr-Shild class. Solutions for spinning objects can be obtained from spherical solutions by the Newman-Janis algorithm. Basic feature of all spinning objects is the existence of the equatorial de Sitter vacuum disk in their deep interiors. Energy conditions distinguish two types of their interiors, preserving or violating the weak energy condition dependently on violation or satisfaction of the energy dominance condition for original spherical solutions. For the 2-nd type the weak energy condition is violated and the interior contains the phantom energy confined by an additional de Sitter vacuum surface. For spinning solitons G-lumps a phantom energy is not screened by horizons and influences their observational signatures, providing a source of information about the scale and properties of a phantom energy. Regular BH remnants and G-lumps can form graviatoms binding electrically charged particles. Their observational signature is the electromagnetic radiation with the frequencies depending on the energy scale of the interior de Sitter vacuum within the range available for observations. A nontrivial observational signature of all DM candidates with de Sitter interiors predicted by analysis of dynamical equations is the induced proton decay in an underground detector like IceCUBE, due to non-conservation of baryon and lepton numbers in their GUT scale false vacuum interiors.

scholarly journals New traversable wormhole solutions in f(T) gravity

2019 ◽  
Vol 28 (04) ◽  
pp. 1950065 ◽  
Author(s):  
R. C. Tefo ◽  
P. H. Logbo ◽  
M. J. S. Houndjo ◽  
J. Tossa
Keyword(s):  
Time Dependence ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Traversable Wormhole ◽  
Torsion Scalar ◽  
Teleparallel Theory ◽  
Text Model ◽  
Spacetime Metric ◽  
Theory Of Gravity ◽  
Modified Formula

In this paper, we search for dynamical traversable wormhole solutions in the modified [Formula: see text] theory of gravity, [Formula: see text] being the torsion scalar. For such a wormhole, the time dependence is inserted in the static traversable wormhole metric of Morris and Thorne. Two set of tetrads are adopted: the diagonal and the nondiagonal tetrads. The diagonal set of tetrads constrains and reduces [Formula: see text] 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 nondynamical spacetime metric, i.e. static traversable wormhole solutions. Moreover we take into account energy condition analysis and the results show that the violation of null energy condition is not determinant for existence of static traversable wormhole solutions.

Stable wormhole models in general relativity under conformal symmetry

2021 ◽  
Vol 18 (03) ◽  
pp. 2150041
Author(s):  
Asifa Ashraf ◽  
Zhiyue Zhang
Keyword(s):  
General Relativity ◽  
Symmetric Space ◽  
Conformal Symmetry ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Anisotropic Fluid ◽  
Spherically Symmetric ◽  
Shape Functions ◽  
The Stability ◽  
Tov Equation

In this study, we shall explore conformal symmetry to examine the wormhole models by considering traceless fluid. In this regard, we shall take anisotropic fluid with spherically symmetric space-time. Further, we shall calculate the properties of shape-functions, which are necessary for the existence of wormhole geometry. The presence of exotic matter is confirmed in all the cases through the violation of the Null Energy Condition. Furthermore, we have discussed the stability of wormhole solutions through the Tolman–Oppenheimer–Volkoff (TOV) equation. It is observed that our acquired solutions are stable under the particular values of involved parameters in different cases in conformal symmetry.

Wormhole solutions via embedding approach in ℛ + βℛ2 gravity with matter coupling

2021 ◽  
Author(s):  
Dan Wang ◽  
G. Mustafa
Keyword(s):  
Shape Function ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Specific Model ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Modified Theories Of Gravity ◽  
Class 1 ◽  
Theory Of Gravity ◽  
Feasible Solutions

In this paper, we examine the embedded wormhole solutions in the modified [Formula: see text] theory of gravity, where [Formula: see text] denotes the trace of the energy–momentum tensor and [Formula: see text] is the Ricci scalar. We derive the embedded class-1 solutions by considering spherically symmetric static spacetime. The shape function is calculated in the framework of embedded class-1 spacetime. It is necessary to mention here that the calculated shape function can be used in other modified theories of gravity. We explore the feasible solutions for the specific model of [Formula: see text] theory of gravity. Energy conditions have been explored using the approach mentioned above. Conclusively, we find that obtained wormhole solutions are acceptable, as the null energy condition is violated in the specific region.

Wormholes supported by f(𝒢) gravity

2014 ◽  
Vol 24 (01) ◽  
pp. 1550003 ◽  
Author(s):  
M. Sharif ◽  
Ayesha Ikram
Keyword(s):  
Power Law ◽  
Energy Momentum Tensor ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Momentum Tensor ◽  
Red Shift ◽  
Energy Conditions ◽  
Shift Function ◽  
Effective Energy ◽  
Barotropic Fluids

This paper is devoted to study the traversable wormhole (WH) solutions in the context of f(𝒢) gravity. For this purpose, we consider the viable power-law form f(𝒢) = a𝒢n as well as specific variable red-shift function and investigate WH geometries for traceless, isotropic as well as barotropic fluids. It is found that in each case, the effective energy-momentum tensor violates the null energy condition throughout the WH throat. We also check the null as well as weak energy conditions for ordinary matter. We conclude that physical acceptable WH solutions exist in certain regions only for radial barotropic case while the range of these regions increases and decreases as the power of 𝒢 increases in even and odd manner, respectively.

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