Narrow Results

The objective of this study is to examine the possible existence of traversable wormhole geometries within the context of $f(R,L_m,T)$ gravity. To meet this objective, we employ the Karmarkar condition to construct the shape function that aids in identifying the wormhole configurations. This developed function is found to satisfy the essential conditions and provides a link between two asymptotically flat spacetime regions. We then assume the Morris–Thorne line element that expresses the wormhole configuration and formulate the anisotropic gravitational equations for a particular minimal matter-spacetime coupled model of the modified theory. Afterward, we develop three solutions and determine their viability by analyzing whether they violate the null energy conditions. Different stability methods are applied to the resulting geometries to explore the acceptance of the considered modified model. We conclude that the developed wormhole structures potentially fulfill the required criteria and thus exist in this modified gravity under all choices of the matter Lagrangian density.

In this paper, I propose a static wormhole model within modified $f(R,T)$ gravity where $f(R,T)=R+2\lambda T$. The wormhole solutions have been evolved in four cases — three different shape function along with redshift $\varphi =\frac{{\varphi }_0}{r}$ and a variable EoS parameter $\omega (r)$ with constant redshift function. I also have explored the energy conditions and the behavior of exotic matter within the wormhole in all scenarios. The presence of exotic matter violates necessary energy conditions near wormhole throat which gives constraint on modified gravity parameter $\lambda$ in all different cases.

High bandwidth and low latency switches are commercially available. Using these switches, it becomes possible to build a system area network to interconnect workstations and processor clusters together to provide a cost-effective parallel computing platform. A processor cluster may be a shared-memory multiprocessor or a mesh-connected multicomputer, etc. The interconnection topology on this kind of platform, called switch-based NOWP, is usually irregular. On such systems, multicast is an important collective communication operation. Two steps are involved in a multicast: (1) the source node sends the multicast message to the destinations which are connected to a switch directly or are the leader of a processor cluster, and (2) the leader node of each cluster sends the message to other destinations in the same cluster. In this paper, we propose two unicast-based multicast algorithms. Algorithm Multicast_1 performs those two steps sequentially; while Algorithm Multicast_2 overlaps them. Performance of the two algorithms will be evaluated and compared.

We obtain a new class of solutions for the Einstein field equations which describe wormholes by using the one-loop effective Lagrangian of quantum electrodynamics. We also show that the derived wormholes can be maintained only by means of a magnetic field.

A class of exact static solution around a global monopole resulting from the breaking of a global SO(3) symmetry is obtained in the context of Lyra geometry.

Our solution is shown to possess an interesting feature like "wormholes" spacetime. It has been shown that the global monopole exerts no gravitational force on surrounding nonrelativistic matter.

We study (3+1) Morris–Thorne wormhole to investigate its thermodynamic properties. It is shown that the wormhole temperature can be evaluated by exploiting Unruh effects. We also propose a possibility of negative temperature originated from exotic matter distribution of the wormhole.

We have investigated the gravitational lensing by two wormholes, viz., Janis–Newman–Winnicour (JNW) wormhole and Ellis wormhole. The deflection angles in the strong field limit are calculated and various lens parameters of two wormholes are compared. It is shown that the JNW wormhole exhibits the relativistic images, while the Ellis wormhole does not have any relativistic image due to the absence of its photon sphere.

A regular wormhole solution in gravity coupled with a phantom scalar and electromagnetic fields is found. The solution exists for a special choice of the parameter f of the potential term. The mass m of a wormhole filled with a phantom and electrostatic fields is calculated. It is shown that close to some point f₀, a small value of the mass m is the remainder of two large masses of the phantom and electrostatic fields. The connection with the renormalization procedure in quantum filed theory is considered. The connection between Wheeler's idea "mass without mass" and renormalization procedure in quantum field theory is discussed.

We consider wormhole solutions in five-dimensional Kaluza–Klein gravity in the presence of a massless ghost four-dimensional scalar field. The system possesses two types of topological nontriviality connected with the presence of the scalar field and of a magnetic charge. Mathematically, the presence of the charge appears in the fact that the S³ part of a spacetime metric is the Hopf bundle S³ →S² with fiber S¹. We show that the fifth dimension spanned on the sphere S¹ is compactified in the sense that asymptotically, at large distances from the throat, the size of S¹ is equal to some constant, the value of which can be chosen to lie, say, in the Planck region. Then, from the four-dimensional point of view, such a wormhole contains a radial magnetic (monopole) field, and an asymptotic four-dimensional observer sees a wormhole with the compactified fifth dimension.

A test particle moving along geodesic line in a spacetime has three physical propagating degrees of freedom and one unphysical gauge degree. We relax the requirement of geodesic completeness of a spacetime. Instead, we require test particles trajectories to be smooth and complete only for physical degrees of freedom. Test particles trajectories for Einstein–Rosen bridge are proved to be smooth and complete in the physical sector, and particles can freely penetrate the bridge in both directions.

In this paper, we study static spherically symmetric wormhole solutions in the framework of f(T) gravity, where T represents torsion scalar. We consider non-diagonal tetrad and anisotropic distribution of the fluid. We construct expressions for matter components such as energy density, radial pressure and transverse pressure from the field equations. Taking into account a particular equation of state (EoS) in terms of traceless fluid, we discuss the behavior of energy conditions for wormhole solutions with well-known f(T) and shape functions. We conclude that physically acceptable static wormhole solutions are obtained for both these functions.

The properties of a dynamic wormhole are investigated. Using a particular equation of state for the fluid on the wormhole throat, we reached an equation of motion for the throat (a hyperbola) that leads to a negative surface energy density σ. The throat expands with the same acceleration 2π|σ| as the Ipser–Sikivie domain wall. We found the Lagrangian leading to the above equation of motion of the throat. The associated Hamiltonian corresponds to a relativistic free particle of a time-dependent negative energy -ℏc/R, where R is the throat radius, similar in form with the Casimir energy inside an expanding spherical box.

In this work, we consider higher-dimensional structures in R²-gravity in an expanding background. We assume a Ricci scalar constant background and use this assumption as the basic constraint to find solutions. Two classes of solutions are presented in which every one includes naked singularity and wormhole geometries. Both classes of solutions show inflationary phase of expansion favored by recent acceleration of the universe. Traversability of the wormhole solutions is discussed. The possibility of satisfying or violating the weak energy condition (WEC) for wormholes is explored. For one class of solutions, particular choices of constants result in wormholes which satisfy the WEC all over the spacetime.

Without reference to exotic sources construction of viable wormholes in Einstein’s general relativity remained ever a myth. With the advent of modified theories, however, specifically the f(R) theory, new hopes arose for the possibility of such objects. From this token, we construct traversable wormholes in f(R) theory supported by a fluid source which respects at least the weak energy conditions. We provide an example (Example 1) of asymptotically flat wormhole in f(R) gravity without ghosts.

For a generic f(R) which admits a polynomial expansion, we find the near-throat wormhole solution. Necessary conditions for the existence of wormholes in such f(R) theories are derived for both zero and nonzero matter sources. For vanishing external sources, we show that the energy conditions are violated. A particular choice of energy–momentum reveals that the wormhole geometry satisfies the weak energy condition (WEC). For a range of parameters, even the strong energy condition (SEC) is shown to be satisfied.

This paper is devoted to the study of static spherically symmetric wormhole solutions along with noncommutative geometry in the background of F(T, T${}_{{𝒢}}$) gravity. We assume a nonzero redshift function as well as two well-known models of this gravity and discuss the behavior of null/weak energy conditions graphically. We conclude that there does not exist any physically acceptable wormhole solution for the first model, but there is a chance to develop physically acceptable wormhole solution in a particular region for the second model.

Previous studies on dynamic wormholes were focused on the dynamics of the wormhole itself, be it either rotating or evolutionary in character and also in various frameworks from classical to braneworld cosmological models. In this work, we modeled a dynamic factor that represents the spatial dynamics in terms of spacetime expansion and contraction surrounding the wormhole itself. Using an RS2-based braneworld cosmological model, we modified the spacetime metric of Wong and subsequently employed the method of Bronnikov, where it is observed that a traversable wormhole is easier to exist in an expanding brane universe, however it is difficult to exist in a contracting brane universe due to stress–energy tensors requirement. This model of spatial dynamic factor affecting the wormhole throat can also be applied on the cyclic or the bounce universe model.

This work looks for new wormhole solutions in the non-conservative Rastall gravity. Although Rastall gravity is considered to be a higher-dimensional gravity, the actual diversion from general relativity essentially happens due to a modification in the corresponding matter tensor part. Thus, it would be interesting to find out if such non-minimal coupling has any effect on the traversable wormholes and their corresponding energy conditions.

This work addresses the question whether exotic matter is essential for the formation of wormholes in modified gravity theories. The basic property of wormhole geometry is the flaring-out condition at the throat which essentially states the violation of null energy condition for the matter threading the wormhole in Einstein gravity. In modified gravity theories, the field equations can be written as Einstein equations with two non-interacting fluids of which one is the usual fluid under consideration and the second term, called the effective matter, comes from the extra geometric terms of the theory. So it is interesting to examine whether normal fluid with restrictions on geometry satisfies the conditions for the formation of wormholes and their stability.

The classical tests of General Relativity, namely, precession of periapsis, deflection of light and time delay serve to establish observational evidence for the theory of general relativity, so they are considered for several spherically symmetric astrophysical objects. In this paper, we investigate a stationary, spherically symmetric wormhole supported by a quintessence polytropic energy satisfying a polytropic equation of state: $p_r=-\omega {\rho }^{1+1/n}$, where $n$ is the polytropic index and $\omega$ is a positive constant such that $1/3<\omega <1$. The solution of such an equation admits the negative null energy, which is the key ingredient for sustaining traversable wormholes. Motivated by the above-mentioned classical tests, we perform similar studies to explore the range of polytropic index $n$ which gives us promising results. The advance of periapsis with respect to a test particle and angle of deflection is calculated graphically for those values of $n$ which cannot be obtained analytically. The time delay has also been calculated numerically and tabulated.