scholarly journals Exploring cylindrical solutions in modified f(G) gravity

2014 ◽  
Vol 92 (12) ◽  
pp. 1528-1540 ◽  
Author(s):  
M.J.S. Houndjo ◽  
M.E. Rodrigues ◽  
D. Momeni ◽  
R. Myrzakulov
Keyword(s):  
Exact Solutions ◽  
Energy Momentum Tensor ◽  
Unit Length ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Momentum Tensor ◽  
Field Equations ◽  
Full System ◽  
Bonnet Gravity ◽  
Cylindrically Symmetric

We present detailed cylindrically symmetric solutions for a type of Gauss–Bonnet gravity. We derive the full system of field equations and show that there exist seven families of exact solutions for three forms of viable models. By applying the method based on the effective fluid energy momentum tensor components, we evaluate the mass per unit length for the solutions. From a dynamical point of the view, by evaluating the null energy condition for these configurations, we show that in some cases the azimuthal pressure breaks the energy condition. This violation of the null energy condition predicts the existence of a cylindrical wormhole.

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 TRAPPING PHOTONS BY A LINE SINGULARITY

2003 ◽  
Vol 12 (06) ◽  
pp. 1095-1112 ◽  
Author(s):  
METIN ARIK ◽  
OZGUR DELICE
Keyword(s):  
Energy Density ◽  
Thin Shell ◽  
Energy Momentum Tensor ◽  
Momentum Tensor ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Cylindrically Symmetric ◽  
Static Solutions ◽  
Line Singularity ◽  
Thick Shells

We present cylindrically symmetric, static solutions of the Einstein field equations around a line singularity such that the energy momentum tensor corresponds to infinitely thin photonic shells. Positivity of the energy density of the thin shell and the line singularity is discussed. It is also shown that thick shells containing mostly radiation are possible in a numerical solution.

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.

Spherically symmetric traversable wormholes in f(R2,T) gravity

2019 ◽  
Vol 16 (10) ◽  
pp. 1950147 ◽  
Author(s):  
M. Zubair ◽  
Quratulien Muneer ◽  
Saira Waheed
Keyword(s):  
Modified Gravity ◽  
Arbitrary Constant ◽  
Energy Momentum Tensor ◽  
Energy Condition ◽  
Momentum Tensor ◽  
Anisotropic Fluid ◽  
Spherically Symmetric ◽  
Matter Distribution ◽  
Field Equations ◽  
Traversable Wormholes

In this paper, we explore the possibility of wormhole solutions existence exhibiting spherical symmetry in an interesting modified gravity based on Ricci scalar term and trace of energy–momentum tensor. For this reason, we assume the matter distribution as anisotropic fluid and a specific viable form of the generic function given by [Formula: see text] involving [Formula: see text] and [Formula: see text], two arbitrary constant parameters. For having a simplified form of the resulting field equations, we assume three different forms of EoS of the assumed matter contents. In each case, we find the numerical wormhole solutions and analyze their properties for the wormhole existence graphically. The graphical behavior of the energy condition bounds is also investigated in each case. It is found that a realistic wormhole solutions satisfying all the properties can be obtained in each case.

Cosmic evolution in the background of R (1 + αQ) gravity

2019 ◽  
Vol 34 (31) ◽  
pp. 1950253 ◽  
Author(s):  
M. Zubair ◽  
M. Zeeshan ◽  
Saira Waheed
Keyword(s):  
Energy Momentum Tensor ◽  
Energy Condition ◽  
Momentum Tensor ◽  
Model Parameters ◽  
Field Equations ◽  
Cosmic Evolution ◽  
Test Particles ◽  
Free Model ◽  
Free Parameters ◽  
Modified Theory

In this paper, we discuss the cosmic evolution in a modified theory involving non-minimal interaction of geometry and matter, labeled as [Formula: see text] gravity, where [Formula: see text] is the non-minimal interaction term. First, we develop the dynamical [Formula: see text] field equations for Friedmann–Lemaitre–Robertson–Walker (FLRW) spacetime and then by using divergence of these equations, we explore its interesting outcome of non-conserved energy–momentum tensor (EMT). The presence of geometry matter coupling in such theories results in non-geodesic test particles motion and hence causes an additional force orthogonal to four-velocity of these particles. By taking these interesting features into account along with a particular choice of Lagrangian [Formula: see text], we explore the resulting expression of energy density. Further, the free model parameters are constrained using energy condition bounds where it is concluded that these values of free parameters are compatible with the recent data.

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.

scholarly journals Compact star in Tolman–Kuchowicz spacetime in the background of Einstein–Gauss–Bonnet gravity

2019 ◽  
Vol 79 (11) ◽  
Author(s):  
Piyali Bhar ◽  
Ksh. Newton Singh ◽  
Francisco Tello-Ortiz
Keyword(s):  
General Relativity ◽  
Energy Momentum Tensor ◽  
Compact Star ◽  
Momentum Tensor ◽  
Energy Conditions ◽  
Coupling Constant ◽  
Field Equations ◽  
Bonnet Gravity ◽  
Principal Directions ◽  
Hilbert Action

Abstract The present work is devoted to the study of anisotropic compact matter distributions within the framework of five-dimensional Einstein–Gauss–Bonnet gravity. To solve the field equations, we have considered that the inner geometry is described by Tolman–Kuchowicz spacetime. The Gauss–Bonnet Lagrangian $$\mathcal {L}_{GB}$$LGB is coupled to the Einstein–Hilbert action through a coupling constant, namely $$\alpha $$α. When this coupling tends to zero general relativity results are recovered. We analyze the effect of this parameter on the principal salient features of the model, such as energy density, radial and tangential pressure and anisotropy factor. These effects are contrasted with the corresponding general relativity results. Besides, we have checked the incidence on an important mechanism: equilibrium by means of a generalized Tolman–Oppenheimer–Volkoff equation and stability through relativistic adiabatic index and Abreu’s criterion. Additionally, the behavior of the subliminal sound speeds of the pressure waves in the principal directions of the configuration and the conduct of the energy-momentum tensor throughout the star are analyzed employing the causality condition and energy conditions, respectively. All these subjects are illuminated by means of physical, mathematical and graphical surveys. The M–I and the M–R graphs imply that the stiffness of the equation of state increases with $$\alpha $$α; however, it is less stiff than GR.

Bianchi type I and V solutions in f(R, T) gravity with time-dependent deceleration parameter

2016 ◽  
Vol 94 (12) ◽  
pp. 1289-1296 ◽  
Author(s):  
M. Zubair ◽  
Syed M. Ali Hassan ◽  
G. Abbas
Keyword(s):  
Deceleration Parameter ◽  
Bianchi Type ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Momentum Tensor ◽  
Type I ◽  
Field Equations ◽  
Bianchi Type I ◽  
Bianchi V ◽  
Type V

In this paper, our attention is to reconstruct an appropriate model for Bianchi type I and Bianchi V space–times in f(R, T) gravity with the help of special law of deceleration parameter in connection to f(R, T) gravity (where R is the Ricci scalar and T is the trace of energy–momentum tensor). We solve the modified Einstein field equations for anisotropic and homogeneous Bianchi type V space–time. The solution of field equations facilitates finding out the physical as well as kinematical quantities. We explore the behavior of null energy condition, energy density, and deceleration parameter to present cosmic picture.

Galactic halo traversable wormhole solutions in f(𝒢,T) gravity

2018 ◽  
Vol 27 (16) ◽  
pp. 1950009 ◽  
Author(s):  
M. Sharif ◽  
Ayesha Ikram
Keyword(s):  
Galactic Halo ◽  
Shape Function ◽  
Energy Momentum Tensor ◽  
Energy Condition ◽  
Null Energy Condition ◽  
Momentum Tensor ◽  
Specific Form ◽  
Spherically Symmetric ◽  
Effective Energy ◽  
Text Model

This paper explores static spherically symmetric wormhole solutions in the galatic halo region for [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 formulate the explicit expressions for matter variables and evaluate wormhole solutions either specifying [Formula: see text] model to construct shape function or taking specific form of the shape function to determine [Formula: see text] model. It is found that null energy condition for the effective energy–momentum tensor is violated throughout the evolution in both cases while physically acceptable wormhole solutions exist only for a considered [Formula: see text] model.

On a non-symmetric theory of the pure gravitational field

1958 ◽  
Vol 54 (1) ◽  
pp. 72-80 ◽  
Author(s):  
D. W. Sciama
Keyword(s):  
Gravitational Field ◽  
Energy Momentum Tensor ◽  
Equations Of Motion ◽  
Rest Mass ◽  
Symmetric Tensor ◽  
Momentum Tensor ◽  
Unified Field Theory ◽  
Field Equations ◽  
Metric Tensor ◽  
Unified Field

ABSTRACTIt is suggested, on heuristic grounds, that the energy-momentum tensor of a material field with non-zero spin and non-zero rest-mass should be non-symmetric. The usual relationship between energy-momentum tensor and gravitational potential then implies that the latter should also be a non-symmetric tensor. This suggestion has nothing to do with unified field theory; it is concerned with the pure gravitational field.A theory of gravitation based on a non-symmetric potential is developed. Field equations are derived, and a study is made of Rosenfeld identities, Bianchi identities, angular momentum and the equations of motion of test particles. These latter equations represent the geodesics of a Riemannian space whose contravariant metric tensor is gij–, in agreement with a result of Lichnerowicz(9) on the bicharacteristics of the Einstein–Schrödinger field equations.

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