scholarly journals New static cylindrical symmetric solutions in GR for unfamiliar EoS parameter values via Noether symmetry

2021 ◽  
Vol 81 (10) ◽  
Author(s):  
Işıl Başaran Öz ◽  
Kazuharu Bamba
Keyword(s):  
Equations Of State ◽  
State Parameter ◽  
Space Time ◽  
Noether Symmetry ◽  
Field Equations ◽  
Eos Parameter ◽  
New Exact Solutions ◽  
Cylindrically Symmetric ◽  
Parameter Values ◽  
Symmetry Method

AbstractThe solutions for the field equations of f(R) gravity are investigated in static cylindrically symmetric space-time. Conserved quantities of the system, as well as unknown functions, can be determined with the help of the Noether symmetry method. In this article, some unknown values of the equations of state parameter (EoS) have emerged as a result of the constraints obtained by analyzing the Noether symmetry equations for the $$f(R)=f_0 R$$ f ( R ) = f 0 R case. Consequently, several new exact solutions have been found for cases of General Relativity in static cylindrically symmetrical space-time for the non-dust matter.

Anisotropic Dark Energy Cosmological Model with Cosmic Strings

2020 ◽  
Author(s):  
T. Vinutha ◽  
V.U.M. Rao ◽  
Molla Mengesha
Keyword(s):  
Dark Energy ◽  
Equation Of State ◽  
Cosmological Model ◽  
State Parameter ◽  
Accelerated Expansion ◽  
Physical Parameters ◽  
Type I ◽  
Field Equations ◽  
Eos Parameter ◽  
Phantom Divide

The present study deals with a spatially homogeneous locally rotationally symmetric (LRS) Bianchi type-I dark energy cosmological model containing one dimensional cosmic string fluid source. The Einstein's field equations are solved by using a relation between the metric potentials and hybrid expansion law of average scale factor. We discuss accelerated expansion of our model through equation of state (ωde) and deceleration parameter (q). We observe that in the evolution of our model, the equation of state parameter starts from matter dominated phase ωde > -1/3 and ultimately attains a constant value in quintessence region (-1 < ωde < -1/3). The EoS parameter of the model never crosses the phantom divide line (ωde = 1). These facts are consistent with recent observations. We also discuss some other physical parameters.

scholarly journals CYLINDRICALLY SYMMETRIC SPINNING BRANS–DICKE SPACE–TIMES WITH CLOSED TIMELIKE CURVES

1999 ◽  
Vol 14 (17) ◽  
pp. 1105-1111 ◽  
Author(s):  
LUIS A. ANCHORDOQUI ◽  
SANTIAGO E. PEREZ BERGLIAFFA ◽  
MARTA L. TROBO ◽  
GRACIELA S. BIRMAN
Keyword(s):  
General Relativity ◽  
Exact Solutions ◽  
Cylindrical Symmetry ◽  
Space Time ◽  
Rigid Rotation ◽  
Closed Timelike Curves ◽  
New Exact Solutions ◽  
Cylindrically Symmetric

We present here three new exact solutions of Brans–Dicke theory for a stationary geometry with cylindrical symmetry in the presence of matter in rigid rotation with [Formula: see text]. All the solutions have eternal closed timelike curves in some region of space–time which has a size that depends on ω. Moreover, two of them do not go over a solution of general relativity in the limit ω→∞.

scholarly journals Anisotropic solution in phantom cosmology via Noether symmetry approach

2018 ◽  
Vol 96 (7) ◽  
pp. 677-680 ◽  
Author(s):  
I. Basaran Oz ◽  
Y. Kucukakca ◽  
N. Unal
Keyword(s):  
Scalar Field ◽  
Bianchi Type ◽  
Space Time ◽  
Noether Symmetry ◽  
Type I ◽  
Field Equations ◽  
Anisotropic Solution ◽  
Bianchi Type I ◽  
Symmetry Approach ◽  
The Universe

In this study, we consider a phantom cosmology in which a scalar field is minimally coupled to gravity. For anisotropic locally rotational symmetric (LRS) Bianchi type I space–time, we use the Noether symmetry approach to determine the potential of such a theory. It is shown that the potential must be in the trigonometric form as a function of the scalar field. We solved the field equations of the theory using the result obtained from the Noether symmetry. Our solution shows that the universe has an accelerating expanding phase.

scholarly journals Cosmic acceleration via space-time-matter theory

2019 ◽  
Vol 34 (36) ◽  
pp. 1950296
Author(s):  
Raziyeh Zaregonbadi
Keyword(s):  
State Parameter ◽  
Space Time ◽  
Cosmic Acceleration ◽  
Late Time ◽  
Field Equations ◽  
Deviation Equation ◽  
Matter Theory ◽  
Induced Field ◽  
Vacuum Spacetime ◽  
The Universe

We consider the space-time-matter theory (STM) in a 5D vacuum spacetime with a generalized FLRW metric to investigate the late-time acceleration of the universe. For this purpose, we derive the 4D induced field equations and obtain the evolution of the state parameter with respect to the redshift. Then, we show that with consideration of the extra dimension scale factor to be a linear function of redshift, this leads to a model which gives an accelerating phase in the universe. Moreover, we derive the geodesic deviation equation in the STM theory to study the relative acceleration of the parallel geodesics of this spacetime, and also, obtain the observer area-distance as a measurable quantity to compare this theory with two other models.

scholarly journals Solutions of weakened field equations in Gödel space-time

2017 ◽  
Vol 37 (2) ◽  
pp. 59
Author(s):  
Aditya Mani Mishra
Keyword(s):  
Field Equation ◽  
Comparative Study ◽  
Scalar Curvature ◽  
Space Time ◽  
Field Equations ◽  
Cylindrically Symmetric

We have solved Weakened field equations, collected work of Lovelock for cylindrically symmetric Gödel type spacetime. A comparative study of these solutions to solution of Einstein’s field equation have shown. Conformality of Gödel spacetime has discussed with vanishing and non-vanishing scalar curvature of the spacetime.

scholarly journals Stable Dyonic Thin-Shell Wormholes in Low-Energy String Theory

2017 ◽  
Vol 2017 ◽  
pp. 1-9 ◽  
Author(s):  
Ali Övgün ◽  
Kimet Jusufi
Keyword(s):  
Electric Charge ◽  
Thin Shell ◽  
Magnetic Charge ◽  
State Parameter ◽  
Stability Domain ◽  
Chaplygin Gas ◽  
Space Time ◽  
Exotic Matter ◽  
The Stability ◽  
Parameter Values

Considerable attention has been devoted to the wormhole physics in the past 30 years by exploring the possibilities of finding traversable wormholes without the need for exotic matter. In particular, the thin-shell wormhole formalism has been widely investigated by exploiting the cut-and-paste technique to merge two space-time regions and to research the stability of these wormholes developed by Visser. This method helps us to minimize the amount of the exotic matter. In this paper, we construct a four-dimensional, spherically symmetric, dyonic thin-shell wormhole with electric charge Q, magnetic charge P, and dilaton charge Σ, in the context of Einstein-Maxwell-dilaton theory. We have applied Darmois-Israel formalism and the cut-and-paste method by joining together two identical space-time solutions. We carry out the dyonic thin-shell wormhole stability analyses by using a linear barotropic gas, Chaplygin gas, and logarithmic gas for the exotic matter. It is shown that, by choosing suitable parameter values as well as equation of state parameter, under specific conditions, we obtain a stable dyonic thin-shell wormhole solution. Finally, we argue that the stability domain of the dyonic thin-shell wormhole can be increased in terms of electric charge, magnetic charge, and dilaton charge.

scholarly journals Post-Newtonian limit: second-order Jefimenko equations

2020 ◽  
Vol 80 (7) ◽  
Author(s):  
David Pérez Carlos ◽  
Augusto Espinoza ◽  
Andrew Chubykalo
Keyword(s):  
Linear Equations ◽  
Space Time ◽  
Second Order ◽  
Field Equations ◽  
Gravitational Fields ◽  
Mass Distributions ◽  
Minkowski Space Time ◽  
Theory Of Gravitation ◽  
Gravity Probe ◽  
Gravitational Equations

Abstract The purpose of this paper is to get second-order gravitational equations, a correction made to Jefimenko’s linear gravitational equations. These linear equations were first proposed by Oliver Heaviside in [1], making an analogy between the laws of electromagnetism and gravitation. To achieve our goal, we will use perturbation methods on Einstein field equations. It should be emphasized that the resulting system of equations can also be derived from Logunov’s non-linear gravitational equations, but with different physical interpretation, for while in the former gravitation is considered as a deformation of space-time as we can see in [2–5], in the latter gravitation is considered as a physical tensor field in the Minkowski space-time (as in [6–8]). In Jefimenko’s theory of gravitation, exposed in [9, 10], there are two kinds of gravitational fields, the ordinary gravitational field, due to the presence of masses, at rest, or in motion and other field called Heaviside field due to and acts only on moving masses. The Heaviside field is known in general relativity as Lense-Thirring effect or gravitomagnetism (The Heaviside field is the gravitational analogous of the magnetic field in the electromagnetic theory, its existence was proved employing the Gravity Probe B launched by NASA (See, for example, [11, 12]). It is a type of gravitational induction), interpreted as a distortion of space-time due to the motion of mass distributions, (see, for example [13, 14]). Here, we will present our second-order Jefimenko equations for gravitation and its solutions.

scholarly journals SPACE–TIME STRUCTURE AND SPINOR GEOMETRY

2008 ◽  
Vol 50 (2) ◽  
pp. 143-176 ◽  
Author(s):  
GEORGE SZEKERES ◽  
LINDSAY PETERS
Keyword(s):  
Cosmological Solution ◽  
Space Time ◽  
Time Structure ◽  
Variation Principle ◽  
Field Equations ◽  
Covering Group ◽  
Space Time Structure ◽  
Spinor Geometry ◽  
Complete Set ◽  
Particle Solution

AbstractThe structure of space–time is examined by extending the standard Lorentz connection group to its complex covering group, operating on a 16-dimensional “spinor” frame. A Hamiltonian variation principle is used to derive the field equations for the spinor connection. The result is a complete set of field equations which allow the sources of the gravitational and electromagnetic fields, and the intrinsic spin of a particle, to appear as a manifestation of the space–time structure. A cosmological solution and a simple particle solution are examined. Further extensions to the connection group are proposed.

scholarly journals Cylindrically Symmetric, Asymptotically Flat, Petrov Type D Spacetime with a Naked Curvature Singularity and Matter Collapse

2017 ◽  
Vol 2017 ◽  
pp. 1-6 ◽  
Author(s):  
Faizuddin Ahmed
Keyword(s):  
Cosmic Time ◽  
Petrov Type ◽  
Energy Conditions ◽  
Anisotropic Fluid ◽  
Curvature Singularity ◽  
Field Equations ◽  
Asymptotically Flat ◽  
Type D ◽  
Cylindrically Symmetric ◽  
Petrov Type D

We present a cylindrically symmetric, Petrov type D, nonexpanding, shear-free, and vorticity-free solution of Einstein’s field equations. The spacetime is asymptotically flat radially and regular everywhere except on the symmetry axis where it possesses a naked curvature singularity. The energy-momentum tensor of the spacetime is that for an anisotropic fluid which satisfies the different energy conditions. This spacetime is used to generate a rotating spacetime which admits closed timelike curves and may represent a Cosmic Time Machine.

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