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.

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 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 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 NON-SINGULAR BLACK-HOLES ON THE BRANE

2004 ◽  
Vol 13 (06) ◽  
pp. 1095-1103 ◽  
Author(s):  
S. SHANKARANARAYANAN ◽  
NARESH DADHICH
Keyword(s):  
Energy Condition ◽  
Null Energy Condition ◽  
Effective Field ◽  
Brane World ◽  
Spherically Symmetric ◽  
Null Condition ◽  
Field Equations ◽  
World Model ◽  
Weyl Curvature ◽  
Black Hole Solutions

We investigate the possibility of obtaining non-singular black-hole solutions in the brane world model by solving the effective field equations for the induced metric on the brane. The Reissner–Nordstrom solution on the brane was obtained by Dadhich et al. by imposing the null energy condition on the 3-brane for a bulk having non-zero Weyl curvature. In this work, we relax the condition of vanishing scalar curvature R, however, retaining the null condition. We have shown that it is possible to obtain a class of static non-singular spherically symmetric brane space–times which admits horizon. We obtain one such class of solution which is a regular version of the Reissner–Nordstrom solution in the standard general relativity.

scholarly journals A new shape function and some specific wormhole solutions in braneworld scenario

2021 ◽  
pp. 2150167
Author(s):  
Bikram Ghosh ◽  
Saugata Mitra
Keyword(s):  
Energy Density ◽  
Shape Function ◽  
Energy Condition ◽  
Energy Conditions ◽  
Shape Functions ◽  
Field Equations ◽  
Strong Energy Condition ◽  
Strong Energy ◽  
Arbitrary Positive Constant ◽  
Anisotropic Case

Considering an energy density of the form [Formula: see text] (where [Formula: see text] is an arbitrary positive constant with dimension of energy density and [Formula: see text]), a shape function is obtained by using field equations of braneworld gravity theory in this paper. Under isotropic scenario wormhole solutions are obtained considering six different redshift functions along with the obtained new shape function. For anisotropic case, wormhole solutions are obtained under the consideration of five different shape functions along with the redshift function [Formula: see text], where [Formula: see text] is an arbitrary constant. In each case all energy conditions are examined and it is found that for some cases all energy conditions are satisfied in the vicinity of the wormhole throat and for the rest of the cases all energy conditions are satisfied except strong energy condition.

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.

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.

scholarly journals Energy bounds in f(R,G) gravity with anisotropic background

2017 ◽  
Vol 14 (12) ◽  
pp. 1750169 ◽  
Author(s):  
M. Farasat Shamir ◽  
Ayesha Komal
Keyword(s):  
Energy Condition ◽  
Gravitational Theory ◽  
Null Energy Condition ◽  
Graphical Analysis ◽  
Gravity Models ◽  
Energy Conditions ◽  
Model Parameters ◽  
Field Equations ◽  
Energy Bounds ◽  
Rotationally Symmetric

This paper investigates the energy bounds in modified Gauss–Bonnet gravity with anisotropic background. Locally rotationally symmetric Bianchi type [Formula: see text] cosmological model in [Formula: see text] gravity is considered to meet this aim. Primarily, a general [Formula: see text] model is used to develop the field equations. In this aspect, we investigate the viability of modified gravitational theory by studying the energy conditions. We take in account four [Formula: see text] gravity models commonly discussed in the literature. We formulate the inequalities obtained by energy conditions and investigate the viability of the above-mentioned models using the Hubble, deceleration, jerk and snap parameters. Graphical analysis shows that for first two [Formula: see text] gravity models, null energy condition (NEC), weak energy condition (WEC) and strong energy condition (SEC) are satisfied under suitable values of anisotropy and model parameters involved. Moreover, SEC is violated for the third and fourth models which predicts the cosmic expansion.

scholarly journals Existence of static wormholes in f(𝒢,T) gravity

2017 ◽  
Vol 27 (01) ◽  
pp. 1750182 ◽  
Author(s):  
M. Sharif ◽  
Ayesha Ikram
Keyword(s):  
Energy Momentum Tensor ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Graphical Analysis ◽  
Momentum Tensor ◽  
Specific Form ◽  
Spherically Symmetric ◽  
Matter Distribution ◽  
Ordinary Matter ◽  
Text Model

This paper investigates static spherically symmetric traversable wormhole (WH) solutions in [Formula: see text] gravity ([Formula: see text] and [Formula: see text] represent the Gauss–Bonnet invariant and trace of the energy–momentum tensor, respectively). We construct explicit expressions for ordinary matter by taking specific form of redshift function and [Formula: see text] model. To analyze the possible existence of wormholes, we consider anisotropic, isotropic, as well as barotropic matter distributions. The graphical analysis shows the violation of null energy condition for the effective energy–momentum tensor throughout the evolution while ordinary matter meets energy constraints in certain regions for each case of matter distribution. It is concluded that traversable WH solutions are physically acceptable in this theory.

Sign in / Sign up

Export Citation Format

Share Document