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Francisco S N Lobo - One of the best experts on this subject based on the ideXlab platform.
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generic spherically symmetric dynamic thin shell traversable Wormholes in standard general relativity
Physical Review D, 2012Co-Authors: Nadiezhda Montelongo Garcia, Francisco S N Lobo, Matt VisserAbstract:We consider the construction of generic spherically symmetric thin-shell traversable wormhole spacetimes in standard general relativity. By using the cut-and-paste procedure, we comprehensively analyze the stability of arbitrary spherically symmetric thin-shell Wormholes to linearized spherically symmetric perturbations around static solutions. While a number of special cases have previously been dealt with in scattered parts of the literature, herein we take considerable effort to make the analysis as general and unified as practicable. We demonstrate in full generality that stability of the wormhole is equivalent to choosing suitable properties for the exotic material residing on the wormhole throat.
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chaplygin traversable Wormholes
Physical Review D, 2006Co-Authors: Francisco S N LoboAbstract:The generalized Chaplygin gas (GCG) is a candidate for the unification of dark energy and dark matter, and is parametrized by an exotic equation of state given by ${p}_{\mathrm{ch}}=\ensuremath{-}A/{\ensuremath{\rho}}_{\mathrm{ch}}^{\ensuremath{\alpha}}$, where $A$ is a positive constant and $0l\ensuremath{\alpha}\ensuremath{\le}1$. In this paper, exact solutions of spherically symmetric traversable Wormholes supported by the GCG are found, possibly arising from a density fluctuation in the GCG cosmological background. To be a solution of a wormhole, the GCG equation of state imposes the following generic restriction $Al(8\ensuremath{\pi}{r}_{0}^{2}{)}^{\ensuremath{-}(1+\ensuremath{\alpha})}$, where ${r}_{0}$ is the wormhole throat radius, consequently violating the null energy condition. The spatial distribution of the exotic GCG is restricted to the throat neighborhood, and the physical properties and characteristics of these Chaplygin Wormholes are further analyzed. Four specific solutions are explored in some detail, namely, that of a constant redshift function, a specific choice for the form function, a constant energy density, and finally, isotropic pressure Chaplygin wormhole geometries.
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stability of phantom Wormholes
Physical Review D, 2005Co-Authors: Francisco S N LoboAbstract:It has recently been shown that traversable Wormholes may be supported by phantom energy. In this work phantom wormhole geometries are modeled by matching an interior traversable wormhole solution, governed by the equation of state $p=\ensuremath{\omega}\ensuremath{\rho}$ with $\ensuremath{\omega}l\ensuremath{-}1$, to an exterior vacuum spacetime at a finite junction interface. The stability analysis of these phantom Wormholes to linearized spherically symmetric perturbations about static equilibrium solutions is carried out. A master equation dictating the stability regions is deduced, and by separating the cases of a positive and a negative surface energy density, it is found that the respective stable equilibrium configurations may be increased by strategically varying the wormhole throat radius. The first model considered, in the absence of a thin shell, is that of an asymptotically flat phantom wormhole spacetime. The second model constructed is that of an isotropic pressure phantom wormhole, which is of particular interest, as the notion of phantom energy is that of a spatially homogeneous cosmic fluid, although it may be extended to inhomogeneous spherically symmetric spacetimes.
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phantom energy traversable Wormholes
Physical Review D, 2005Co-Authors: Francisco S N LoboAbstract:It has been suggested that a possible candidate for the present accelerated expansion of the Universe is ``phantom energy''. The latter possesses an equation of state of the form $\ensuremath{\omega}\ensuremath{\equiv}p/\ensuremath{\rho}l\ensuremath{-}1$, consequently violating the null energy condition. As this is the fundamental ingredient to sustain traversable Wormholes, this cosmic fluid presents us with a natural scenario for the existence of these exotic geometries. 'Note, however, that the notion of phantom energy is that of a homogeneously distributed fluid. Nevertheless, it can be extended to inhomogeneous spherically symmetric spacetimes, and it is shown that traversable Wormholes may be supported by phantom energy. Because of the fact of the accelerating Universe, macroscopic Wormholes could naturally be grown from the submicroscopic constructions that originally pervaded the quantum foam. One could also imagine an advanced civilization mining the cosmic fluid for phantom energy necessary to construct and sustain a traversable wormhole. In this context, we investigate the physical properties and characteristics of traversable Wormholes constructed using the equation of state $p=\ensuremath{\omega}\ensuremath{\rho}$, with $\ensuremath{\omega}l\ensuremath{-}1$. We analyze specific wormhole geometries, considering asymptotically flat spacetimes and imposing an isotropic pressure. We also construct a thin shell around the interior wormhole solution, by imposing the phantom energy equation of state on the surface stresses. Using the ``volume integral quantifier'' we verify that it is theoretically possible to construct these geometries with vanishing amounts of averaged null energy condition violating phantom energy. Specific wormhole dimensions and the traversal velocity and time are also deduced from the traversability conditions for a particular wormhole geometry. These phantom energy traversable Wormholes have far-reaching physical and cosmological implications. For instance, an advanced civilization may use these geometries to induce closed timelike curves, consequently violating causality.
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morris thorne Wormholes with a cosmological constant
Physical Review D, 2003Co-Authors: Francisco S N Lobo, Jose P S Lemos, Sergio Quinet De OliveiraAbstract:First, the ideas introduced in the wormhole research field since the work of Morris and Thorne are reviewed, namely, the issues of energy conditions, wormhole construction, stability, time machines and astrophysical signatures. Then, spherically symmetric and static traversable Morris-Thorne Wormholes in the presence of a generic cosmological constant $\ensuremath{\Lambda}$ are analyzed. A matching of an interior solution to the unique exterior vacuum solution is done using directly the Einstein equations. The structure as well as several physical properties and characteristics of traversable Wormholes due to the effects of the cosmological term are studied. Interesting equations appear in the process of matching. For instance, one finds that for asymptotically flat and anti\char21{}de Sitter spacetimes the surface tangential pressure $\mathcal{P}$ of the thin shell, at the boundary of the interior and exterior solutions, is always strictly positive, whereas for de Sitter spacetime it can take either sign as one would expect, being negative (tension) for relatively high $\ensuremath{\Lambda}$ and high wormhole radius, positive for relatively high mass and small wormhole radius, and zero in between. Finally, some specific solutions with $\ensuremath{\Lambda},$ based on the Morris-Thorne solutions, are provided.
Matt Visser - One of the best experts on this subject based on the ideXlab platform.
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generic spherically symmetric dynamic thin shell traversable Wormholes in standard general relativity
Physical Review D, 2012Co-Authors: Nadiezhda Montelongo Garcia, Francisco S N Lobo, Matt VisserAbstract:We consider the construction of generic spherically symmetric thin-shell traversable wormhole spacetimes in standard general relativity. By using the cut-and-paste procedure, we comprehensively analyze the stability of arbitrary spherically symmetric thin-shell Wormholes to linearized spherically symmetric perturbations around static solutions. While a number of special cases have previously been dealt with in scattered parts of the literature, herein we take considerable effort to make the analysis as general and unified as practicable. We demonstrate in full generality that stability of the wormhole is equivalent to choosing suitable properties for the exotic material residing on the wormhole throat.
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geometric structure of the generic static traversable wormhole throat
Physical Review D, 1997Co-Authors: David Hochberg, Matt VisserAbstract:Traversable Wormholes have traditionally been viewed as intrinsically topological entities in some multiply connected spacetime. Here, we show that topology is too limited a tool to accurately characterize a generic traversable wormhole: in general one needs geometric information to detect the presence of a wormhole, or more precisely to locate the wormhole throat. For an arbitrary static spacetime we shall define the wormhole throat in terms of a 2–dimensional constant-time hypersurface of minimal area. (Zero trace for the extrinsic curvature plus a “flare–out” condition.) This enables us to severely constrain the geometry of spacetime at the wormhole throat and to derive generalized theorems regarding violations of the energy conditions—theorems that do not involve geodesic averaging but nevertheless apply to situations much more general than the spherically symmetric Morris–Thorne traversable wormhole. [For example: the null energy condition (NEC), when suitably weighted and integrated over the wormhole throat, must be violated.] The major technical limitation of the current approach is that we work in a static spacetime—this is already a quite rich and complicated system.
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lorentzian Wormholes from einstein to hawking
1995Co-Authors: Matt VisserAbstract:Preface Acknowledgments I. Background: 1. Introduction 2. General Relativity 3. Quantum Field Theory 4. Units and Natural Scales II. History: 5. The Einstein-Rosen Bridge 6. Spacetime Foam 7. The Kerr Wormhole 8. The Cosmological Constant 9. Wormhole Taxonomy 10. Interregnum III. Renaissance: 11. Traversible Wormholes 12. Energy Conditions 13. Engineering Considerations 14. Thin Shells: Fromalism 15. Thin Shells: Wormholes 16. Topological Censorship IV.: Time Travel: 17. Chronology: Basic Notions 18. From Wormhole to Time Machine 19. Response to the Paradoxes V. Quantum Effects 20. Semiclassical Quantum Gravity 21. van Vleck Determinants: Formalism 22. van Vleck Determinants: Wormholes 23. Singularity Structure 24. Minisuperspace Wormholes VI. Reprise: 25. Where We Stand Bibliography Index
Mustapha Azregainou - One of the best experts on this subject based on the ideXlab platform.
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from static to rotating to conformal static solutions rotating imperfect fluid Wormholes with out electric or magnetic field
European Physical Journal C, 2014Co-Authors: Mustapha AzregainouAbstract:We derive a shortcut stationary metric formula for generating imperfect fluid rotating solutions, in Boyer–Lindquist coordinates, from spherically symmetric static ones. We explore the properties of the curvature scalar and stress–energy tensor for all types of rotating regular solutions we can generate without restricting ourselves to specific examples of regular solutions (regular black holes or Wormholes). We show through examples how it is generally possible to generate an imperfect fluid regular rotating solution via radial coordinate transformations. We derive rotating Wormholes that are modeled as imperfect fluids and discuss their physical properties. These are independent on the way the stress–energy tensor is interpreted. A solution modeling an imperfect fluid rotating loop black hole is briefly discussed. We then specialize to the recently discussed stable exotic dust Ellis wormhole as emerged in a source-free radial electric or magnetic field, and we generate its, conjecturally stable, rotating counterpart. This turns out to be an exotic imperfect fluid wormhole, and we determine the stress–energy tensor of both the imperfect fluid and the electric or magnetic field.
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from static to rotating to conformal static solutions rotating imperfect fluid Wormholes with out electric or magnetic field
arXiv: General Relativity and Quantum Cosmology, 2014Co-Authors: Mustapha AzregainouAbstract:We derive a shortcut stationary metric formula for generating imperfect fluid rotating solutions, in Boyer-Lindquist coordinates, from spherically symmetric static ones. We explore the properties of the curvature scalar and stress-energy tensor for all types of rotating regular solutions we can generate without restricting ourselves to specific examples of regular solutions (regular black holes or Wormholes). We show through examples how it is generally possible to generate an imperfect fluid regular rotating solution via radial coordinate transformations. We derive rotating Wormholes that are modeled as imperfect fluids and discuss their physical properties that are independent on the way the stress-energy tensor is interpreted. A solution modeling an imperfect fluid rotating loop black hole is briefly discussed. We then specialize to the recently discussed stable exotic dust Ellis wormhole emerged in a source-free radial electric or magnetic field, generate its, conjecturally stable, rotating counterpart which turns out to be an exotic imperfect fluid wormhole and determine the stress-energy tensor of both the imperfect fluid and the electric or magnetic field.
Jose P S Lemos - One of the best experts on this subject based on the ideXlab platform.
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cylindrical Wormholes
Physical Review D, 2009Co-Authors: K A Bronnikov, Jose P S LemosAbstract:It is shown that the existence of static, cylindrically symmetric Wormholes does not require violation of the weak or null energy conditions near the throat, and cylindrically symmetric wormhole geometries can appear with less exotic sources than Wormholes whose throats have a spherical topology. Examples of exact wormhole solutions are given with scalar, spinor and electromagnetic fields as sources, and these fields are not necessarily phantom. In particular, there are wormhole solutions for a massless, minimally coupled scalar field in the presence of a negative cosmological constant, and for an azimuthal Maxwell electromagnetic field. All these solutions are not asymptotically flat. A no-go theorem is proved, according to which a flat (or string) asymptotic behavior on both sides of a cylindrical wormhole throat is impossible if the energy density of matter is everywhere nonnegative.
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morris thorne Wormholes with a cosmological constant
Physical Review D, 2003Co-Authors: Francisco S N Lobo, Jose P S Lemos, Sergio Quinet De OliveiraAbstract:First, the ideas introduced in the wormhole research field since the work of Morris and Thorne are reviewed, namely, the issues of energy conditions, wormhole construction, stability, time machines and astrophysical signatures. Then, spherically symmetric and static traversable Morris-Thorne Wormholes in the presence of a generic cosmological constant $\ensuremath{\Lambda}$ are analyzed. A matching of an interior solution to the unique exterior vacuum solution is done using directly the Einstein equations. The structure as well as several physical properties and characteristics of traversable Wormholes due to the effects of the cosmological term are studied. Interesting equations appear in the process of matching. For instance, one finds that for asymptotically flat and anti\char21{}de Sitter spacetimes the surface tangential pressure $\mathcal{P}$ of the thin shell, at the boundary of the interior and exterior solutions, is always strictly positive, whereas for de Sitter spacetime it can take either sign as one would expect, being negative (tension) for relatively high $\ensuremath{\Lambda}$ and high wormhole radius, positive for relatively high mass and small wormhole radius, and zero in between. Finally, some specific solutions with $\ensuremath{\Lambda},$ based on the Morris-Thorne solutions, are provided.
Ali Ovgun - One of the best experts on this subject based on the ideXlab platform.
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the effect of the brane dicke coupling parameter on weak gravitational lensing by Wormholes and naked singularities
Physical Review D, 2019Co-Authors: Wajiha Javed, Rimsha Babar, Ali OvgunAbstract:In this paper, we analyze the deflection angle of light by Brane-Dicke wormhole in the weak field limit approximation to find the effect of the Brane-Dicke coupling parameter on the weak gravitation lensing. For this purpose, we consider new geometric techniques, i.e., Gauss-Bonnet theorem and optical geometry in order to calculate the deflection angle. Furthermore, we verify our results by considering the most familiar geodesic technique. Moreover, we establish the quantum corrected metric of Brane-Dicke wormhole by replacing the classical geodesic with Bohmian trajectories, whose matter source and anisotropic pressure are influenced by Bohmian quantum effects and calculate its quantum corrected deflection angle. Then, we calculate the deflection angle by naked singularities and compare with the result of wormhole's. Such a novel lensing feature might serve as a way to detect Wormholes, naked singularities and also the evidence of Brane-Dicke theory.
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arxiv gravitational lensing by rotating Wormholes
Physical Review D, 2018Co-Authors: Kimet Jusufi, Ali OvgunAbstract:In this paper the deflection angle of light by a rotating Teo wormhole spacetime is calculated in the weak limit approximation. We mainly focus on the weak deflection angle by revealing the gravitational lensing as a partially global topological effect. We apply the Gauss-Bonnet theorem (GBT) to the optical geometry osculating the Teo-Randers wormhole optical geometry to calculate the deflection angle. Furthermore we find the same result using the standard geodesic method. We have found that the deflection angle can be written as a sum of two terms, namely the first term is proportional to the throat of the wormhole and depends entirely on the geometry, while the second term is proportional to the spin angular momentum parameter of the wormhole. A direct observation using lensing can shed light and potentially test the nature of rotating Wormholes by comparing with the black holes systems.
