Narrow Results

This work aims to explore the possibility of wormholes (WHs) fenced by fuzzy Dark Matter (FDM) haloes relying on the Einasto density profile (EDP). The research explains how combining the EDP with an anisotropic stress-energy momentum tensor leads to the formation of WH solutions corresponding to different Einasto index values. We have investigated the existence of fuzzy WHs and developed the shape function for them. An analysis is conducted on the active gravitational mass and the lodging diagrams for a certain form of the shape function. Additionally, we have also examined the exotic matter’s breach of the null energy conditions, the equilibrium conditions, and the complexity factor associated with the fuzzy WHs.

In this paper, we explore the possibility of formation of a traversable wormhole in General Relativity supported by particle creation mechanism. The repulsive back-reaction pressure generated through this mechanism can be thought of as a source of sustaining a traversable wormhole. In the first part of this paper, we model a wormhole geometry by assuming an inverse powerlaw variation of particle creation pressure within the wormhole geometry, and the shape function for the wormhole is obtained, assuming a finite redshift function. By stabilizing the wormhole structure, based on the causality of sound-speed we obtained the existence range of the parameter $\beta$ associated with particle creation mechanism. The general shape function obtained is found to adhere to the feasibility conditions of a viable wormhole geometry. Then we studied the 2D and 3D embedding derived for the obtained shape function. In the second part of the paper, we followed the reverse approach of the aforementioned treatment, where we derived the particle creation pressures by assuming three commonly utilized toy shape-functions. The energy conditions are then investigated for all these cases. In essence, particle creation phenomena inside the wormhole may indeed provide for the possibility of sustenance of stable wormhole structure.

In this paper, we investigate the possibility of using closed timelike curves (CTCs) in relativistic hypercomputation. We introduce a wormhole based hypercomputation scenario which is free of the common worries, such as the blueshift problem. We also discuss the physical reasonability of our scenario, and why we cannot simply ignore the possibility of the existence of spacetimes containing CTCs.

We present three different theoretically foreseen, but unusual, astrophysical situations where the gravitational lens equation ends up being the same, thus producing a degeneracy problem. These situations are: (a) the case of gravitational lensing by exotic stresses (matter violating the weak energy condition and thus having a negative mass, particular cases of wormhole solutions can be used as an example), (b) scalar field gravitational lensing (i.e. when considering the appearance of a scalar charge in the lensing scenario), and (c) gravitational lensing in closed universes (with antipodes). The reasons that lead to this degeneracy in the lens equations, the possibility of actually encountering it in the real universe, and eventually the ways to break it, are discussed.

It is shown that among the different classes of claimed static wormhole solutions of the vacuum Brans–Dicke theory only Brans Class I solution with coupling constant ω less than -1.5 (excluding the point ω = 2) gives rise to physically viable traversable wormhole geometry. Usability of this wormhole geometry for interstellar travel has been examined.

Some new class of Chaplygin wormholes are investigated in the framework of a Chaplygin gas with the equation of state . Since empty spacetime (p = ρ = 0) does not follow Chaplygin gas, so the interior Chaplygin wormhole solutions will never be asymptotically flat. For this reason, we have to match our interior wormhole solution with an exterior vacuum solution, i.e. Schwarzschild solution at some junction interface, say r = a. We also discuss the total amount of matter characterized by Chaplygin gas that supplies fuel to construct a wormhole.

It is proved that all thin-shell wormholes built from two identical regions of vacuum static, spherically symmetric spacetimes have a negative shell surface energy density in any scalar–tensor theory of gravity with a non-ghost massless scalar field and a non-ghost graviton.

A recent work by Dey and Sen derived the approximate light deflection angle α by an Ellis wormhole in terms of proper radial distance ℓ that covers the entire spacetime. On the other hand, Bodenner and Will calculated the expressions for light bending in Schwarzschild geometry using various coordinates and showed that they all reduce to a single formula when re-expressed in the coordinate independent language of "circumferential radius" r_C identified with the standard radial coordinate r_S. We shall argue that the coordinate invariant language for two-way wormholes should be ℓ rather than r_S. Hence here we find the exact deflection α in Ellis wormhole geometry first in terms of ℓ and then in terms of r_S. We confirm the latter expression using three different methods. We argue that the practical measurement scheme does not necessarily single out either ℓ or r_S. Some errors in the literature are corrected.

In this study, energy distributions of the various wormholes which connect two different parts of the universe have been investigated. We have obtained the energies of several types of wormholes as the statical wormholes, wormholes with scalar fields, electrical charged wormholes, zero density wormholes, zero radial tides wormholes, conformal wormholes, inflating wormholes, wormhole model in the Friedmann–Robertson–Walker (FRW) cosmology and Visser–Kar–Dadlich (VKD) wormholes using the Einstein, Weinberg and Landau–Lifshitz energy–momentum prescriptions. The Weinberg and Landau–Lifshitz energies of the statical wormholes, wormholes with scalar fields, electrical charged wormholes, zero density wormholes, zero radial tides wormholes or VKD-wormholes give the same results. Also, Weinberg, Landau–Lifshitz and Einstein energies of the conformal wormholes, inflating wormholes or wormholes in the FRW-cosmology give the different results.

A fundamental ingredient in wormhole physics is the presence of exotic matter, which involves the violation of the null energy condition. Although a plethora of wormhole solutions have been explored in the literature, it is useful to find geometries that minimize the usage of exotic matter. In this work, we find exact wormhole solutions in Brans–Dicke theory where the normal matter threading the wormhole satisfies the null energy condition throughout the geometry. Thus, the latter implies that it is the effective stress–energy tensor containing the scalar field, that plays the role of exotic matter, that is responsible for sustaining the wormhole geometry. More specifically, we consider a zero redshift function and a particular choice for the scalar field and determine the remaining quantities, namely, the stress–energy tensor components and the shape function. The solution found is not asymptotically flat, so that this interior wormhole spacetime needs to be matched to an exterior vacuum solution.

Eddington-inspired Born–Infeld (EiBI) gravity is a recently proposed modified theory of gravity, based on the classic work of Eddington and Born–Infeld nonlinear electrodynamics. In this paper, we consider the possibility that wormhole geometries are sustained in EiBI gravity. We present the gravitational field equations for an anisotropic stress–energy tensor and consider the generic conditions, for the auxiliary metric, at the wormhole throat. In addition to this, we obtain an exact solution for an asymptotically flat wormhole.

In this study, we investigate whether global monopoles cause black holes or wormholes to form. Field equations for static spherically symmetric spacetimes with global monopoles are obtained in $f(R)$ gravity. We found exact solutions for the field equations without using any perturbation or approximation methods. It is shown that the obtained $f(R)$ function is in accordance with the $\mathrm{\Lambda }$-cold dark matter ($\mathrm{\Lambda }$-CDM) model. Also, it is shown that the static spherically symmetric spacetimes associated with global monopoles form black holes or wormhole structures under some restrictions. Finally, geometrical and physical results of the solutions are discussed.

We construct wormhole-like solutions in type IIA string theory. These solutions represent wormholes in four dimensions and are given by the D2-branes within appropriated backgrounds fields. We present the conditions on these fields which lead to the four-dimensional wormholes. In the special case, we show how the particular solution in type IIA theory leads to the dynamic wormhole. We also speculate about the number of universes and the cosmological constant.

The electron magnetic moment decomposition calculated in QED is proposed to have origin in a multi-vortex internal structure of the electron. This proposition is founded on two important contributions of this work. First, a critical review on Weyl model of electron, Einstein–Rosen bridge and Wheeler’s wormholes leads to a new idea of a topological defect in cylindrical spacetime geometry as a natural representation of the electron. A concrete realization of this idea in terms of the derivation of a new vortex-metric, and its physical interpretation to establish the geometric origin of the electron magnetic moment decomposition constitute the second contribution. Remarkable occurrence of a vortex structure in the basis mode function used in BLFQ is also pointed out indicating wider ramification of the proposed electron model.

It is known that wormhole geometry could be found solving the Einstein field equations by tolerating the violation of null energy condition (NEC). Violation of NEC is not possible for the physical matter distributions, however, it can be achieved by considering distributions of “exotic matter”. The main purpose of this work is to find generating functions comprising the wormhole-like geometry and discuss the nature of these generating functions. We have used the Herrera et al. [Phys. Rev. D77, 027502 (2008)] approaches of obtaining generating functions in the background of wormhole spacetime. Here we have adopted two approaches for solving the field equations to find wormhole geometry. In the first method, we have assumed the redshift function f(r) and the shape function b(r) and solve for the generating functions. In another attempt, we assume generating functions and redshift functions and then try to find shape functions of the wormholes.

In this study, we explore the spherically symmetric static wormhole solutions in the Rastall modified theory of gravity. For this, we consider the anisotropic fluid distribution to construct the field equations for Rastall background. Further, we calculate the matter density function and pressure components for anisotropic fluid from the field equations. Furthermore, we employ the traceless fluid by using a particular equation of state (EoS) to analyze the necessary properties of shape function for wormholes and behavior of energy bounds. However, the major purpose of this study is to acquire the wormhole solutions for traceless fluid in the Rastall background. Moreover, we examine the stability of different forces acting on the system. At the end, it is concluded that our solutions under this current scenario are physically acceptable.

Noncommutative geometry, an offshoot of string theory, replaces point-like objects by smeared objects. The resulting uncertainty may cause a black hole to be observationally indistinguishable from a traversable wormhole, while the latter, in turn, may become observationally indistinguishable from a gravastar. The same noncommutative-geometry background allows the theoretical construction of thin-shell wormholes from gravastars and may even serve as a model for dark energy.

In this work, the possible existence of wormhole solutions have been investigated in the extended teleparallel $f(T)$ theory of gravity by incorporating the Lorentzian source of non-commutative geometry through the conformal motion. The physical concept of conformal symmetry becomes more arguable when it is discussed in the background of non-commutative geometry, especially with the Lorentzian source. In this context, two specific different models of the extended teleparallel theory, that is, $f_1(T)={\eta }_{1}T+\frac{{\eta }_2}{T}$, and $f_2(T)={\eta }_3{T}^n$ (where ${\eta }_1$, ${\eta }_2$, ${\eta }_3$ being real constants and $n$ a positive integer) have been studied. The corresponding energy conditions are worked out and are analyzed graphically in the presence of the conformal motion with Lorentzian source. The presence of the exotic matter has been confirmed due to the violation of null energy conditions under some particular conditions, thereby proving the existence of the wormhole geometries in both of the models under investigation. Moreover, the stability of the wormhole geometries via the Tolman-Oppenheimer-Volkov equation has been discussed. It is concluded that these wormhole solutions supported by the non-exotic matter truly exist and are well stable under the extended teleparallel gravity.

In this paper, we have discussed a (1 + 9)-dimensional open cosmological model motivated from N = 2 maximal supergravity arguments characterized by the presence of a wormhole connected to the extra dimensions part and a Gauss–Bonnet (GB) curvature corrections. The universe is dominated by dark energy and cold dark matter (CDM) which emerged from extra dimensions as supported by recent phenomenological and observational arguments. By assuming that the wormhole in the outer/inner regions of the halos of galaxies is characterized by a CDM profile density, it was revealed that the universe is expanding acceleratedly with time, dominated by a microscopic traversable wormhole and dark energy. The role of the dominance of the GB term is discussed and the model is confronted with astrophysical observations.

We review some recent results concerning the properties of static, spherically symmetric configurations in RS2 type brane worlds: 1) Solving the trace of the effective 4D gravity equations, we obtain general classes of black hole and wormhole metrics, including families which unify symmetric wormholes, extremal black holes and non-extremal non-singular black holes. 2) Assuming (where is a part of the 5D Weyl tensor contributing to the 4D gravity equations), we show that material scalar fields confined on the brane may violate the no-hair theorem, support wormholes or form particlelike objects, but only at super-nuclear matter densities in the strong field region. 3) Solutions to the bulk field equations are found in case , among them solutions with a nonzero 4D cosmological constant, generalizing the so-called "black string".