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So-called regular black holes are a topic currently of considerable interest in the general relativity and astrophysics communities. Herein we investigate a particularly interesting regular black hole spacetime described by the line element [ ds^{2}=-left(1-frac{2m}{sqrt{r^{2}+a^{2}}}right)dt^{2}+frac{dr^{2}}{1-frac{2m}{sqrt{r^{2}+a^{2}}}} +left(r^{2}+a^{2}right)left(dtheta^{2}+sin^{2}theta ;dphi^{2}right). ] This spacetime neatly interpolates between the standard Schwarzschild black hole and the Morris-Thorne traversable wormhole; at intermediate stages passing through a black-bounce (into a future incarnation of the universe), an extremal null-bounce (into a future incarnation of the universe), and a traversable wormhole. As long as the parameter $a$ is non-zero the geometry is everywhere regular, so one has a somewhat unusual form of regular black hole, where the origin $r=0$ can be either spacelike, null, or timelike. Thus this spacetime generalizes and broadens the class of regular black holes beyond those usually considered.
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Based on the recently introduced black-bounce spacetimes, we shall consider the construction of the related spherically symmetric thin-shell traversable wormholes within the context of standard general relativity. All of the really unusual physics is encoded in one simple parameter $a$ which characterizes the scale of the bounce. Keeping the discussion as close as possible to standard general relativity is the theorists version of only adjusting one feature of the model at a time. We shall modify the standard thin-shell traversable wormhole construction, each bulk region now being a black-bounce spacetime, and with the physics of the thin shell being (as much as possible) derivable from the Einstein equations. Furthermore, we shall apply a dynamical analysis to the throat by considering linearized radial perturbations around static solutions, and demonstrate that the stability of the wormhole is equivalent to choosing suitable properties for the exotic material residing on the wormhole throat. The construction is sufficiently novel to be interesting, and sufficiently straightforward to be tractable.
A possible candidate for the present accelerated expansion of the Universe is phantom energy, which possesses an equation of state of the form $omegaequiv p/rho<-1$, 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. In this context, we shall construct phantom wormhole geometries by matching an interior wormhole solution, governed by the phantom energy equation of state, to an exterior vacuum at a junction interface. Several physical properties and characteristics of these solutions are further investigated. The dynamical stability of the transition layer of these phantom wormholes to linearized spherically symmetric radial perturbations about static equilibrium solutions is also explored. It is found that the respective stable equilibrium configurations may be increased by strategically varying the wormhole throat radius.
We study a traversable wormhole originated by a transformation over the 4D Dymnikova metric which describes analytic Black-Holes (BH). By using a transformation of coordinates which is adapted from the used in the Einstein-Rosen bridge, we study a specific family of geodesics in which a test particle with non-zero electric charge induces an effective magnetic monopole, that is perceived by observers outside the wormhole. Because the Riemannian geometry cannot explain the presence of magnetic monopoles, then we propose a torsional geometry in order to explore the possibility that magnetic monopoles can be geometrically induced. We obtain an expression that relates torsion and magnetic fields jointly with a Dirac-like expression for magnetic and electric charges, such that torsion makes possible define a fundamental length that provides a magnetic field and a spacetime discretization.
The current interests in the universe motivate us to go beyond Einsteins General theory of relativity. One of the interesting proposals comes from a new class of teleparallel gravity named symmetric teleparallel gravity, i.e., $f(Q)$ gravity, where the non-metricity term $Q$ is accountable for fundamental interaction. These alternative modified theories of gravitys vital role are to deal with the recent interests and to present a realistic cosmological model. This manuscripts main objective is to study the traversable wormhole geometries in $f(Q)$ gravity. We construct the wormhole geometries for three cases: (i) by assuming a relation between the radial and lateral pressure, (ii) considering phantom energy equation of state (EoS), and (iii) for a specific shape function in the fundamental interaction of gravity (i.e. for linear form of $f(Q)$). Besides, we discuss two wormhole geometries for a general case of $f(Q)$ with two specific shape functions. Then, we discuss the viability of shape functions and the stability analysis of the wormhole solutions for each case. We have found that the null energy condition (NEC) violates each wormhole model which concluded that our outcomes are realistic and stable. Finally, we discuss the embedding diagrams and volume integral quantifier to have a complete view of wormhole geometries.
The motion of spinning test particles around a traversable wormhole is investigated using the Mathisson Papapetrous Dixon equations, which couple the Riemann tensor with the antisymmetric tensor $S^{ab}$, related to the spin of the particle. Hence, we study the effective potential, circular orbits, and innermost stable circular orbit ISCO of spinning particles. We found that the spin affects significantly the location of the ISCO, in contrast with the motion of nonspinning particles, where the ISCO is the same in both the upper and lower universes. On the other hand, since the dynamical fourmomentum and kinematical fourvelocity of the spinning particle are not always parallel, we also consider a superluminal bound on the particles motion. In the case of circular orbits at the ISCO, we found that the motion of particles with an adimensional spin parameter lower greater than $s=-1.5$ $(1.5)$ is forbidden. The spin interaction becomes important for Kerr black hole orbiting super massive wormholes SMWH.
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