scholarly journals Wormhole Models and Energy Conditions in f ℛ Gravity with the Hu–Sawicki Model

2020 ◽  
Vol 2020 ◽  
pp. 1-12
Author(s):  
Ouziala Ikram ◽  
G. Mustafa
Keyword(s):  
Equation Of State ◽  
Symmetric Space ◽  
Shape Function ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Space Time ◽  
Energy Conditions ◽  
Fluid Distribution ◽  
Anisotropic Fluid ◽  
Nature Of Matter

In this recent study, we shall investigate the wormhole models with a Hu–Sawicki model in the framework of f ℛ gravity. Spherically static symmetric space-time is considered to construct wormhole models with the anisotropic fluid distribution. The traceless matter is discussed by imposing a particular equation of state. To address the important conditions of the shape function of the wormhole geometry, we have used the particular values of the involved parameters. Furthermore, different energy conditions are discussed to check the nature of matter against two specific models. The null energy condition is observed to be violated for both of the models. It is mentioned that our inquired results are acceptable.

scholarly journals Stable Wormholes in the Background of an Exponential f(R) Gravity

Universe ◽  
2020 ◽  
Vol 6 (4) ◽  
pp. 48 ◽  
Author(s):  
Ghulam Mustafa ◽  
Ibrar Hussain ◽  
M. Farasat Shamir
Keyword(s):  
Stability Analysis ◽  
Equation Of State ◽  
Shape Function ◽  
Energy Condition ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Spherically Symmetric ◽  
Shape Functions ◽  
Spacetime Geometry ◽  
Specific Shape

The current paper is devoted to investigating wormhole solutions with an exponential gravity model in the background of f ( R ) theory. Spherically symmetric static spacetime geometry is chosen to explore wormhole solutions with anisotropic fluid source. The behavior of the traceless matter is studied by employing a particular equation of state to describe the important properties of the shape-function of the wormhole geometry. Furthermore, the energy conditions and stability analysis are done for two specific shape-functions. It is seen that the energy condition are to be violated for both of the shape-functions chosen here. It is concluded that our results are stable and realistic.

Wormhole models with exotic matter in Rastall gravity

2020 ◽  
Vol 17 (10) ◽  
pp. 2050146
Author(s):  
G. Mustafa ◽  
Tie-Cheng Xia
Keyword(s):  
Shape Function ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Exotic Matter ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Shape Functions ◽  
Anisotropic Models ◽  
Specific Shape

In this paper, we examine the wormhole solutions by taking two different anisotropic models in Rastall gravity. For this purpose, we shall discuss anisotropic fluid to construct two different anisotropic models. Further, we shall employ two specific shape functions to calculate the behavior of energy conditions. The presence of exotic matter is confirmed in all the cases of this study due to the violation of the null energy condition. All the properties of shape function under both anisotropic models are fulfilled. It is noticed that wormhole solutions exist under the particular values of involved parameters in different cases in Rastall gravity.

scholarly journals Dark Energy Stars with Quadratic Equation of State

2019 ◽  
Author(s):  
Manuel Malaver ◽  
Hamed Kasmaei
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Energy Condition ◽  
Scalar Fields ◽  
Quadratic Equation ◽  
Accelerated Expansion ◽  
Fluid Distribution ◽  
Anisotropic Fluid ◽  
Field Equations ◽  
Quadratic Equation Of State

Recent astronomical observations with respect to measurements in distant supernovas, cosmic microwave background and weak gravitational lensing confirm that the Universe is undergoing a phase of accelerated expansion and it has been proposed that this cosmological behavior is caused by a hypothetical dark energy which has a strong negative pressure that allows explain the expanding universe. Several theoretical ideas and models related dark the energy includes the cosmological constant, quintessence, Chaplygin gas, braneworld and tachyonic scalar fields. In this paper, we have obtained new relativistic stellar configurations considering an anisotropic fluid distribution with a charge distribution which could represents a potential model of a dark energy star. In order to investigate the effect of a quadratic equation of state in this anisotropic model we specify particular forms for the gravitational potential that allow solving the Einstein-Maxwell field equations. For these new solutions we checked that the radial pressure, metric coefficients, energy density, anisotropy factor, charge density , mass function are well defined and are regular in the interior of the star. The solutions found can be used in the development of dark energy stars models satisfying all physical acceptability conditions but the causality condition and strong energy condition are violated. We expect that these models have multiple applications in astrophysics and cosmology.

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.

scholarly journals Traversable wormholes and energy conditions with two different shape functions in f(R) gravity

2019 ◽  
Vol 28 (02) ◽  
pp. 1950039 ◽  
Author(s):  
Nisha Godani ◽  
Gauranga C. Samanta
Keyword(s):  
Energy Density ◽  
Shape Function ◽  
Energy Condition ◽  
State Parameter ◽  
Null Energy Condition ◽  
Energy Conditions ◽  
Radial Coordinate ◽  
Shape Functions ◽  
Anisotropic Parameter ◽  
Traversable Wormholes

Traversable wormholes, tunnel-like structures introduced by Morris and Thorne [Am. J. Phys. 56 (1988) 395], have a significant role in connection of two different spacetimes or two different parts of the same spacetime. The characteristics of these wormholes depend upon the redshift and shape functions which are defined in terms of radial coordinate. In literature, several shape functions are defined and wormholes are studied in [Formula: see text] gravity with respect to these shape functions [F. S. N. Lobo and M. A. Oliveira, Phys. Rev. D 80 (2009) 104012; H. Saiedi and B. N. Esfahani, Mod. Phys. Lett. A 26 (2011) 1211; S. Bahamonde, M. Jamil, P. Pavlovic and M. Sossich, Phys. Rev. D 94 (2016) 044041]. In this paper, two shape functions (i) [Formula: see text] and (ii) [Formula: see text], [Formula: see text], are considered. The first shape function is newly defined, however, the second one is collected from the literature [M. Cataldo, L. Liempi and P. Rodríguez, Eur. Phys. J. C 77 (2017) 748]. The wormholes are investigated for each type of shape function in [Formula: see text] gravity with [Formula: see text], where [Formula: see text], [Formula: see text], [Formula: see text] and [Formula: see text] are real constants. Varying the parameter [Formula: see text] or [Formula: see text], [Formula: see text] model is studied in five subcases for each type of shape function. In each case, the energy density, radial and tangential pressures, energy conditions that include null energy condition, weak energy condition, strong energy condition and dominated energy condition and anisotropic parameter are computed. The energy density is found to be positive and all energy conditions are obtained to be violated which support the existence of wormholes. Also, the equation-of-state parameter is obtained to possess values less than [Formula: see text], that shows the presence of the phantom fluid and leads toward the expansion of the universe.

scholarly journals A study of traversable wormhole solutions in extended teleparallel theory of gravity with matter coupling

2021 ◽  
Vol 81 (10) ◽  
Author(s):  
Allah Ditta ◽  
Ibrar Hussain ◽  
G. Mustafa ◽  
Abdelghani Errehymy ◽  
Mohammed Daoud
Keyword(s):  
Shape Function ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Graphical Analysis ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Modified Theories Of Gravity ◽  
Class 1 ◽  
Theories Of Gravity ◽  
T Tau

AbstractThis study is devoted to explore the physical aspects of wormhole geometry under embedded class-1 spacetime in $$f(T,\tau )$$ f ( T , τ ) gravity, where $$\tau $$ τ denotes the trace of the energy-momentum tensor and T is the torsion. 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. To complete this study, we take diagonal and off-diagonal tetrad, and try to build a comparison by considering the validity region of energy conditions in embedded class-1 spacetime. The embedded surface diagram is given to understand the connection between the two different regions of spacetime. The validity regions of all the energy conditions are calculated. A detailed graphical analysis is provided for validity regions of all the energy conditions. The presence of exotic matter is confirmed in both the cases as the null energy condition is violated.

scholarly journals On the Nature of Exotic Matter in Morris-Thorne Wormholes

2020 ◽  
Vol 4 (3) ◽  
Author(s):  
Peter K F Kuhfittig ◽  
Keyword(s):  
Equation Of State ◽  
Shape Function ◽  
Energy Condition ◽  
Radial Pressure ◽  
Phantom Energy ◽  
Null Energy Condition ◽  
Exotic Matter ◽  
Typical Shape

It is well known that phantom energy, which is characterized by the equation of state p = ωρ, ω < −1, can support Morris-Thorne wormholes since it leads to a violation of the null energy condition. The purpose of this note is to show that the converse is also true in the following sense: for a typical shape function, the equation of state of exotic matter in the vicinity of the throat is given by p↓r = ωρ, ω < −1, where pr is the radial pressure.

scholarly journals Traversable wormholes in Einsteinian cubic gravity

2019 ◽  
Vol 35 (06) ◽  
pp. 2050017 ◽  
Author(s):  
Mohammad Reza Mehdizadeh ◽  
Amir Hadi Ziaie
Keyword(s):  
Equation Of State ◽  
Gravitational Lensing ◽  
Energy Condition ◽  
Higher Order ◽  
Energy Conditions ◽  
Geodesic Motion ◽  
De Sitter ◽  
Asymptotically Flat ◽  
Traversable Wormholes ◽  
Standard Energy

In this work, we investigate wormhole configurations described by a constant redshift function in Einstein-Cubic gravity ( ECG ). We derive analytical wormhole geometries by assuming a particular equation of state ( EoS ) and investigate the possibility that these solutions satisfy the standard energy conditions. We introduce exact asymptotically flat and anti-de Sitter (AdS) spacetimes that admit traversable wormholes. These solutions are obtained by imposing suitable values for the parameters of the theory so that the resulted geometries satisfy the weak energy condition ( WEC ) in the vicinity of the throat, due to the presence of higher-order curvature terms. Moreover, we find that AdS solutions satisfy the WEC throughout the spacetime. A description of the geodesic motion of time-like and null particles is presented for the obtained wormhole solutions. Also, using gravitational lensing effects, observational features of the wormhole structure are discussed.

scholarly journals Traversable wormholes with exponential shape function in modified gravity and general relativity: A comparative study

2020 ◽  
Vol 29 (09) ◽  
pp. 2050068 ◽  
Author(s):  
Gauranga C. Samanta ◽  
Nisha Godani ◽  
Kazuharu Bamba
Keyword(s):  
General Relativity ◽  
Equation Of State ◽  
Comparative Study ◽  
Modified Gravity ◽  
Shape Function ◽  
Anisotropy Parameter ◽  
Energy Conditions ◽  
Traversable Wormholes

We have proposed a novel shape function on which the metric that models traversable wormholes is dependent. Using this shape function, the energy conditions, equation-of-state and anisotropy parameter are analyzed in [Formula: see text] gravity, [Formula: see text] gravity and general relativity. Furthermore, the consequences obtained with respect to these theories are compared. In addition, the existence of wormhole geometries is investigated.

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