Stability of Non-asymptotically Flat Thin-Shell Wormholes in Generalized Dilaton-Axion Gravity

We construct a new type of thin-shell wormhole for non-asymptotically flat charged black holes in generalized dilaton-axion gravity inspired by low-energy string theory using cut-and-paste technique. We have shown that this thin shell wormhole is stable. The most striking feature of our model is that the total amount of exotic matter needed to support the wormhole can be reduced as desired with the suitable choice of the value of a parameter. Various other aspects of thin-shell wormhole are also analyzed.     

Thin shell wormholes in higher dimensional Einstein–Maxwell theory

We construct thin shell Lorentzian wormholes in higher dimensional Einstein–Maxwell theory applying the ‘Cut and Paste’ technique proposed by Visser. The linearized stability is analyzed under radial perturbations around some assumed higher dimensional spherically symmetric static solution of the Einstein field equations in presence of Electromagnetic field. We determine the total amount of exotic matter, which is concentrated at the wormhole throat.     

A New Class of Stable (2+1) Dimensional Thin Shell Wormhole

Few years ago, Bañados, Teitelboim and Zanelli (BTZ) (in Phys. Rev. Lett. 69:1849 (1992)) has discovered an explicit vacuum solution of (2+1)-dimensional gravity with negative cosmological constant. It has been argued that the existence of such physical systems with an event horizon and thermodynamic properties similar to (3+1) dimensional black holes. These vacuum solutions of (2+1)-dimensional gravity are asymptotically anti-de Sitter and are known as BTZ black holes. We provide a new type of thin-shell stable wormhole from the BTZ black holes. This is the first example of stable thin shell wormhole in (2+1)-dimension. Several characteristics of this thin-shell wormhole have been discussed.     

A theoretical construction of thin shell wormhole from tidal charged black hole

Recently, Dadhich et al. (Phys. Lett. B 487, 1, 2000) have discovered a black hole solution localized on a three brane in five dimensional gravity in the Randall–Sundrum scenario. In this article, we develop a new class of thin shell wormhole by surgically grafting above two black hole spacetimes. Various aspects of this thin wormhole are also analyzed.     

A spherically symmetric radiating shell in the presence of a spinless radiating central body

We construct a solution of Einstein's field equations with a possible astrophysical interest by matching a Vaidya solution with another Vaidya solution through a thin spherical shell of radially radiating matter. We study the system of equations for the motion of the shell and the radiation fields in two simple cases. In one of them we consider a dust shell of constant proper mass radiating at constant rate. In the other case we restrict the motion of the shell to a stationary configuration and assume it to be totally opaque. We find that this later solution is unstable under small perturbations in the radius of the shell but there exist stable stationary solutions if the pressure within the shell is different from zero.     

Thin-Shell Wormholes from Regular Charged Black Holes

We investigate a new thin-shell wormhole constructed by surgically grafting two regular charged black holes arising from the action using nonlinear electrodynamics coupled to general relativity. The stress-energy components within the shell violate the null and weak energy conditions but obey the strong energy condition. Several other aspects of this thin-shell wormhole are also analyzed. The most important finding is that the presence of a charge is essential for producing a thin-shell wormhole that is stable to linearized spherically symmetric perturbations about a static equilibrium solution. The precise conditions depend on various properties of the black hole.     

Boosted cylindrical magnetized Kaluza–Klein wormhole

In this work, we consider a vacuum solution of Kaluza–Klein theory with cylindrical symmetry. We investigate the physical properties of the solution as viewed in four dimensional spacetime, which turns out to be a stationary, cylindrical wormhole supported by a scalar field and a magnetic field oriented along the wormhole. We then apply a boost to the five dimensional solution along the extra dimension, and perform the Kaluza–Klein reduction. As a result, we show that the new solution is still a wormhole with a radial electric field and a magnetic field stretched along the wormhole throat.     

Nonsymmetric dynamical thin-shell wormhole in Robinson–Trautman class

The thin-shell wormhole created using the Darmois–Israel formalism applied to Robinson–Trautman family of spacetimes is presented. The stress energy tensor created on the throat is interpreted in terms of two dust streams and it is shown that asymptotically this wormhole settles to the Schwarzschild wormhole with a throat located at the position of the horizon. This behavior shows a nonlinear stability (within the Robinson–Trautman class) of this spherically symmetric wormhole. The gravitational radiation emitted by the Robinson–Trautman wormhole during the transition to spherical symmetry is indistinguishable from that of the corresponding black hole Robinson–Trautman spacetime. Subsequently, we show that the higher-dimensional generalization of Robinson–Trautman geometry offers a possibility of constructing wormholes without the need to violate the energy conditions for matter induced on the throat.     

Stability of Charged Thin-Shell Wormholes in (2+1) Dimensions

In this paper we construct charged thin-shell wormholes in (2+1)-dimensions applying the cut-and-paste technique implemented by Visser, from a BTZ black hole which was discovered by Bañados, Teitelboim and Zanelli (Phys. Rev. Lett. 69:1849, 1992), and the surface stress are determined using the Darmois-Israel formalism at the wormhole throat. We analyzed the stability of the shell considering phantom-energy or generalised Chaplygin gas equation of state for the exotic matter at the throat. We also discussed the linearized stability of charged thin-shell wormholes around the static solution.     

Non-commutative wormholes exhibiting conformal motion in Rastall gravity

In the present paper, we explore the existence of wormhole solutions using conformal symmetries in Rastall theory of gravity. For this purpose, we take spherical symmetric model filled with matter distribution as anisotropic fluid. For the sake of simplifications, we consider the energy density profiles of Gaussian and Lorentzian distributions of non-commutative geometry. Using both these distributions, we obtain analytic wormhole solutions in terms of some special math functions like gamma, exponential and hypergeometric functions. For graphical illustrations, we take some appropriate choices of the free parameters along with different values of Rastall parameter. It is seen that in both cases, the obtained wormhole solutions satisfy the basic criteria of wormhole existence. Further, we describe the possible constraints for the positivity of active gravitational mass in both distributions. We also explore the stability of obtained wormholes solutions by utilizing the modified equilibrium condition in terms of four different forces in Rastall theory. It is concluded that the constructed solutions are stable and physically viable.     

Traversable braneworld wormholes supported by astrophysical observations

In this study, we investigate the characteristics and properties of a traversable wormhole constrained by the current astrophysical observations in the framework of modified theories of gravity (MOG). As a concrete case, we study traversable wormhole space–time configurations in the Dvali–Gabadadze–Porrati (DGP) braneworld scenario, which are supported by the effects of the gravity leakage of extra dimensions. We find that the wormhole space–time structure will open in terms of the 2σ confidence level when we utilize the joint constraints supernovae (SNe) Ia + observational Hubble parameter data (OHD) + Planck + gravitational wave (GW) and z < 0:2874. Furthermore, we obtain several model-independent conclusions, such as (i) the exotic matter threading the wormholes can be divided into four classes during the evolutionary processes of the universe based on various energy conditions; (ii) we can offer a strict restriction to the local wormhole space–time structure by using the current astrophysical observations; and (iii) we can clearly identify a physical gravitational resource for the wormholes supported by astrophysical observations, namely the dark energy components of the universe or equivalent space–time curvature effects from MOG. Moreover, we find that the strong energy condition is always violated at low redshifts.     

A positive cosmological constant in string theory through AdS/CFT wormholes

There are two important examples of physical systems which violate the strong energy condition: Universes (like, it would seem, our own) with a positive cosmological constant, and wormholes. We suggest that a positive cosmological constant can be reconciled with string theory by considering wormholes in string backgrounds. This is argued in two directions: first, we show that brane-worlds with positive cosmological constants give rise to bulk singularities which are best resolved by embedding the brane-world in an AdS/CFT wormhole; and second, for the simplest kind of wormhole in an asymptotically AdS space, we show that the IR stability of the matter needed to keep the wormhole open requires the presence of a brane-world. UV stability conditions then forbid a negative cosmological constant on the brane-world.     

A new stability criterion for general cylindrical thin-shell wormholes

The paper deals with a detailed study of the stability criteria for general static cylindrical thin-shell wormhole.The stability analysis is done under perturbations preserving the symmetry for two definitions of the throat of the wormhole separately. Finally, the stability conditions are discussed both geometrically and physically.     

Stability of Einstein-power-Maxwell (2+1)-dimensional wormholes

This paper is devoted to the study of stable and unstable geometrical structures of charged thin-shell wormholes constructed from Einstein-power-Maxwell black holes by using Visser cut and paste approach. We use Israel thin-shell formalism to evaluate the stress-energy tensor components of matter distribution located at the wormhole throat. The stability of thin-shell is investigated by using equations of state (phantom-like and generalized Chaplygin gas model) for exotic matter and radial perturbation about equilibrium throat radius. We conclude that stable regions increase by increasing the charge parameter.     

Morris–Thorne wormhole with Karmarkar condition

In this paper, we construct a wormhole shape function by using Karmarkar condition. We observe that our proposed shape function connects two asymptotically flat regions, which shows the existence of Morris–Thorne traversable wormhole. Moreover, we also represent the embedding diagram in three-dimensional Euclidean space which can be extended from throat to infinity. Further, the Null and Weak energy conditions are discussed in detail. With this shape function, the anisotropic factor exhibits a repulsive nature at the throat. We support all the analysis of this work through graphical representation. It is concluded that our proposed model fulfills all the necessary conditions and shows the existence of exotic matter in the formulism of wormhole geometry in the context of General Relativity.     

Wormhole supported by dark energy admitting conformal motion

In this article, we study the possibility of sustaining static and spherically symmetric traversable wormhole geometries admitting conformal motion in Einstein gravity, which presents a more systematic approach to search a relation between matter and geometry. In wormhole physics, the presence of exotic matter is a fundamental ingredient and we show that this exotic source can be dark energy type which support the existence of wormhole spacetimes. In this work we model a wormhole supported by dark energy which admits conformal motion. We also discuss the possibility of the detection of wormholes in the outer regions of galactic halos by means of gravitational lensing. Studies of the total gravitational energy for the exotic matter inside a static wormhole configuration are also performed.     

Synthesis,characterization and visible-light driven photocatalysis by differently structured CdS/ZnS sandwich and core–shell nanocomposites

CdS/ZnS sandwich and core–shell nanocomposites were synthesized by a simple and modified Chemical Precipitation method under ambient conditions. The synthesized composites were characterized by XRD, SEM, TEM, EDAX and FTIR. Optical properties were analyzed by UV–vis. Spectroscopy and the photoluminescence study was done to monitor the recombination of photo-generated charge-carriers. Thermal stability of the synthesized composites was analyzed by Thermal Gravimetric Analysis (TGA). XRD revealed the formation of nanocomposites as mixed diffraction peaks were observed in the XRD pattern. SEM and TEM showed the morphology of the nanocomposites particles and their fine particle size. EDAX revealed the appropriate molar ratios exhibited by the constituent elements in the composites and FTIR gave some characteristic peaks which indicated the formation of CdS/ZnS nanocomposites. Electrochemical Impedance Spectroscopy was done to study charge transfer properties along the nanocomposites. Photocatalytic properties of the synthesized composites were monitored by the photocatalytic kinetic study of Acid Blue dye and p-chlorophenol under visible light irradiation. Results revealed the formation of stable core–shell nanocomposites and their efficient photocatalytic properties.     

Wavefunction of Wormhole in the Einstein-Yang-Mills Theory

In this paper, the wavefunction of wormhole in the Einstein-Yang-Mills theory is presented by using the method proposed by Hawking. Analysing the wavefunction obtained, we find that the probability density of quantum wormhole at a = 0 is zero and there is the most probable radius for the ground-state wavefunction of wormhole. It indicates that the quantum wormhole is stable.     

Motion of charged particles in a NUTty Einstein–Maxwell spacetime and causality violation

We investigate the motion of electrically charged test particles in spacetimes with closed timelike curves, a subset of the black hole or wormhole Reissner–Nordström-NUT spacetimes without periodic identification of time. We show that, while in the wormhole case there are closed worldlines inside a potential well, the wordlines of initially distant charged observers moving under the action of the Lorentz force can never close or self-intersect. This means that for these observers causality is preserved, which is an instance of our weak chronology protection criterion.