Conformal and traversable wormholes with monopole and perfect fluid in f(R)-gravity

2016 ◽  
Vol 25 (02) ◽  
pp. 1650017 ◽  
Author(s):  
Dog̃ukan Taṣer ◽  
Melis Ulu Dog̃ru
Keyword(s):  
Perfect Fluid ◽  
Modified Gravity ◽  
Conformal Symmetry ◽  
Phantom Energy ◽  
Spherically Symmetric ◽  
Global Monopole ◽  
Field Equations ◽  
Traversable Wormholes ◽  
Symmetry Properties ◽  
Symmetric Spacetime

We investigate spherically symmetric spacetime filled with global monopole and perfect fluid in [Formula: see text]-gravity. We consider field equations of [Formula: see text]-gravity in order to understand the global monopole and the perfect fluid curve to the spacetime. It has taken advantages of conformal symmetry properties of the spacetime to solve these equations. The obtained solutions are improved in case of phantom energy. It is shown that obtained [Formula: see text] function is consistent with well-known models of the modified gravity. Also, it is examined whether the obtained solutions support a traversable wormhole geometry. Obtained results of the solutions have been concluded.

Higher-dimensional gravitational collapse of perfect fluid spherically symmetric spacetime in f(R, T) gravity

2018 ◽  
Vol 33 (12) ◽  
pp. 1850065 ◽  
Author(s):  
Suhail Khan ◽  
Muhammad Shoaib Khan ◽  
Amjad Ali
Keyword(s):  
Perfect Fluid ◽  
Outer Region ◽  
Energy Tensor ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Higher Dimensional ◽  
Stress Energy ◽  
Inner Region ◽  
Symmetric Spacetime ◽  
Spherically Symmetric Spacetime

In this paper, our aim is to study (n + 2)-dimensional collapse of perfect fluid spherically symmetric spacetime in the context of f(R, T) gravity. The matching conditions are acquired by considering a spherically symmetric non-static (n + 2)-dimensional metric in the inner region and Schwarzschild (n + 2)-dimensional metric in the outer region of the star. To solve the field equations for above settings in f(R, T) gravity, we choose the stress–energy tensor trace and the Ricci scalar as constants. It is observed that two physical horizons, namely, cosmological and black hole horizons appear as a consequence of this collapse. A singularity is also formed after the birth of both the horizons. It is also observed that the term f(R0, T0) slows down the collapsing process.

scholarly journals GRAVITATIONAL FIELD OF A GLOBAL MONOPOLE IN A MODIFIED GRAVITY

2011 ◽  
Vol 03 ◽  
pp. 446-454 ◽  
Author(s):  
T. R. P. CARAMÊS ◽  
E. R. BEZERRA DE MELLO ◽  
M. E. X. GUIMARÃES
Keyword(s):  
Gravitational Field ◽  
Modified Gravity ◽  
Field Approximation ◽  
Weak Field ◽  
Symmetric System ◽  
Radial Coordinate ◽  
Spherically Symmetric ◽  
Global Monopole ◽  
Field Equations ◽  
Metric Tensor

In this paper we analyze the gravitational field of a global monopole in the context of f(R) gravity. More precisely, we show that the field equations obtained are expressed in terms of [Formula: see text]. Since we are dealing with a spherically symmetric system, we assume that F(R) is a function of the radial coordinate only. Moreover, adopting the weak field approximation, we can provide all components of the metric tensor. A comparison with the corresponding results obtained in General Relativity and in the Brans-Dicke theory is also made.

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.

Conformal cylindrically symmetric spacetimes in modified gravity

2015 ◽  
Vol 30 (37) ◽  
pp. 1550202 ◽  
Author(s):  
Murat Metehan Türkog̃lu ◽  
Melis Ulu Dog̃ru
Keyword(s):  
Scalar Field ◽  
Perfect Fluid ◽  
Casimir Force ◽  
Conformal Symmetry ◽  
Vacuum State ◽  
Field Equations ◽  
Cylindrically Symmetric ◽  
Symmetric Spacetimes ◽  
Cylindrically Symmetric Spacetime ◽  
Symmetric Spacetime

We investigate cylindrically symmetric spacetimes in the context of [Formula: see text] gravity. We firstly attain conformal symmetry of the cylindrically symmetric spacetime. We obtain solutions to use features of the conformal symmetry, field equations and their solutions for cylindrically symmetric spacetime filled with various cosmic matters such as vacuum state, perfect fluid, anisotropic fluid, massive scalar field and their combinations. With the vacuum state solutions, we show that source of the spacetime curvature is considered as Casimir effect. Casimir force for given spacetime is found using Wald’s axiomatic analysis. We expose that the Casimir force for Boulware, Hartle–Hawking and Unruh vacuum states could have attractive, repulsive and ineffective features. In the perfect fluid state, we show that matter form of the perfect fluid in given spacetime must only be dark energy. Also, we offer that potential of massive and massless scalar field are developed as an exact solution from the modified field equations. All solutions of field equations for vacuum case, perfect fluid and scalar field give a special [Formula: see text] function convenient to [Formula: see text]-CDM model. In addition to these solutions, we introduce conformal cylindrical symmetric solutions in the cases of different [Formula: see text] models. Finally, geometrical and physical results of the solutions are discussed.

Conformal symmetric Bianchi type-I cosmologies in f(R) gravity

2018 ◽  
Vol 33 (23) ◽  
pp. 1850134 ◽  
Author(s):  
Dog̃ukan Taṣer ◽  
Melis Ulu Dog̃ru
Keyword(s):  
Perfect Fluid ◽  
Bianchi Type ◽  
Conformal Symmetry ◽  
Cosmological Models ◽  
Value Of Time ◽  
Type I ◽  
Field Equations ◽  
Bianchi Type I ◽  
Symmetry Properties ◽  
Bianchi Type I Universe

In this study, we investigate the Bianchi type-I cosmologies with string cloud attached to perfect fluid in f(R) gravity. The field equations and their exact solutions for Bianchi type-I cosmologies with string cloud attached to a perfect fluid are found by using the conformal symmetry properties. The obtained solutions under the varied selection of arbitrary constants indicate three cosmological models. Isotropy conditions for obtained cosmological models are investigated for large value of time. Whether or not the string cloud in conformal symmetric Bianchi type-I universe supports the isotropy condition for the large value of time has been investigated. Also, we examine the contracting and decelerating features of the obtained solutions by using Raychaudhuri equation. Finally, geometrical and physical results of the solutions are discussed.

scholarly journals ON THE MOTION OF A TEST PARTICLE AROUND A GLOBAL MONOPOLE IN A MODIFIED GRAVITY

2012 ◽  
Vol 27 (30) ◽  
pp. 1250177 ◽  
Author(s):  
T. R. P. CARAMÊS ◽  
E. R. BEZERRA DE MELLO ◽  
M. E. X. GUIMARÃES
Keyword(s):  
Test Particle ◽  
Modified Gravity ◽  
Functional Form ◽  
Weak Field ◽  
Radial Coordinate ◽  
Spherically Symmetric ◽  
Global Monopole ◽  
Field Equations ◽  
Metric Tensor ◽  
Spherically Symmetric Metric

In this paper we suggest an approach to analyze the motion of a test particle in the spacetime of a global monopole within a f(R)-like modified gravity. The field equations are written in a simplified form in terms of [Formula: see text]. Since we are dealing with a spherically symmetric metric, we express F(R) as a function of the radial coordinate only, e.g., [Formula: see text]. So, the choice of a specific form for f(R) will be equivalent to adopt an Ansatz for [Formula: see text] . By choosing an explicit functional form for [Formula: see text], we obtain the weak field solutions for the metric tensor also compute the time-like geodesics and analyze the motion of a massive test particle. An interesting feature is an emerging attractive force exerted by the monopole on the particle.

Stability of charged neutron star in Palatini f(R) gravity

2019 ◽  
Vol 34 (31) ◽  
pp. 1950252 ◽  
Author(s):  
M. Z. Bhatti ◽  
Z. Yousaf ◽  
Zarnoor
Keyword(s):  
Chemical Composition ◽  
Neutron Star ◽  
Modified Gravity ◽  
Equilibrium Equation ◽  
Hydrostatic Equilibrium ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Symmetric Geometry ◽  
The Stability ◽  
Tov Equation

In this work, we discuss the stability of charged neutron star in the background of [Formula: see text] gravity and construct the generalized Tolman–Oppenheimer–Volkoff (TOV) equations. For this, we consider static spherically symmetric geometry to construct the hydrostatic equilibrium equation and deduce TOV equations from modified field equations with electromagnetic effects. We conclude that the generalized TOV equation depicts the stable stars configuration independent of the generic function of the modified gravity if the condition of uniform entropy and chemical composition is assumed.

scholarly journals GRAVITATIONAL COLLAPSE OF SPHERICALLY SYMMETRIC PERFECT FLUID WITH KINEMATIC SELF-SIMILARITY

2002 ◽  
Vol 11 (02) ◽  
pp. 155-186 ◽  
Author(s):  
C. F. C. BRANDT ◽  
L.-M. LIN ◽  
J. F. VILLAS DA ROCHA ◽  
A. Z. WANG
Keyword(s):  
Black Holes ◽  
Perfect Fluid ◽  
Gravitational Collapse ◽  
Spherically Symmetric ◽  
De Sitter ◽  
Einstein Field Equations ◽  
Field Equations ◽  
Self Similarity ◽  
Schwarzschild Solution ◽  
Naked Singularities

Analytic spherically symmetric solutions of the Einstein field equations coupled with a perfect fluid and with self-similarities of the zeroth, first and second kinds, found recently by Benoit and Coley [Class. Quantum Grav.15, 2397 (1998)], are studied, and found that some of them represent gravitational collapse. When the solutions have self-similarity of the first (homothetic) kind, some of the solutions may represent critical collapse but in the sense that now the "critical" solution separates the collapse that forms black holes from the collapse that forms naked singularities. The formation of such black holes always starts with a mass gap, although the "critical" solution has homothetic self-similarity. The solutions with self-similarity of the zeroth and second kinds seem irrelevant to critical collapse. Yet, it is also found that the de Sitter solution is a particular case of the solutions with self-similarity of the zeroth kind, and that the Schwarzschild solution is a particular case of the solutions with self-similarity of the second kind with the index α=3/2.

scholarly journals Nonstatic Spherically Symmetric Solutions for a Perfect Fluid in General Relativity

1976 ◽  
Vol 29 (2) ◽  
pp. 113 ◽  
Author(s):  
N Chakravarty ◽  
SB Dutta Choudhury ◽  
A Banerjee
Keyword(s):  
General Relativity ◽  
Exact Solutions ◽  
Perfect Fluid ◽  
Dynamical Behaviour ◽  
Symmetric Distribution ◽  
Spherically Symmetric ◽  
Field Equations ◽  
Spherically Symmetric Solutions ◽  
Spherically Symmetric Distribution ◽  
General Method

A general method is described by which exact solutions of Einstein's field equations are obtained for a nonstatic spherically symmetric distribution of a perfect fluid. In addition to the previously known solutions which are systematically derived, a new set of exact solutions is found, and the dynamical behaviour of the corresponding models is briefly discussed.

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