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The self-energy and self-force for particles with electric and scalar charges at rest in the space-time of massless and massive wormholes are considered. The particle with electric charge is always attracted to wormhole throat for arbitrary profile of the throat. The self-force for scalar particle shows different behavior depending on the non-minimal coupling. The self-force for massive scalar field is localized close to the throat of the wormhole.

The purpose of this paper is to test the validity of the thin shell formalism. Firstly, we construct a dust thick shell collapsing to a Schwarzschild black hole. From this exact solution, we show that the two sides of the shell satisfy different equations of motion. Moreover, we show that the inner side and the outer side always cross each other right after the formation of the thin shell, causing a breakdown of the model. Secondly, we establish a class of wormholes with non-zero thickness and extremal Reissner-Nordström exterior. In the thin shell limit, we find that the surface stress-energy tensor contains the contribution of electromagnetic field, which contradicts the assumption in previous literature.

We study shadows cast, under some circumstances, by a certain class of rotating wormholes and explore the dependence of the shadows on the wormhole spin. We compare our results with that of a Kerr black hole. For small spin, the shapes of the shadows cast by a wormhole and a black hole are nearly identical to each other. However, with increasing values of the spin, the shape of a wormhole shadow start deviating considerably from that of a Kerr black hole. Detection of such considerable deviation in future observations may possibly indicate the presence of a wormhole. In other words, our results indicate that the wormholes which are considered in our work and have reasonable spin can be distinguished from a black hole, through the observation of their shadows.

In this work, we explore wormhole geometries in a recently proposed modified gravity theory arising from a non-conservative gravitational theory, tentatively denoted action-dependent Lagrangian theories. The generalized gravitational field equation essentially depends on a background four-vector λ^μ, that plays the role of a coupling parameter associated with the dependence of the gravitational Lagrangian upon the action, and may generically depend on the spacetime coordinates. Considering wormhole configurations, by using “Buchdahl coordinates”, we find that the four-vector is given by λ_μ = (0, 0, λ_θ, 0), and that the spacetime geometry is severely restricted by the condition gttguu = −1, where u is the radial coordinate. We find a plethora of specific asymptotically flat, symmetric and asymmetric, solutions with power law choices for the function λ, by generalizing the Ellis-Bronnikov solutions and the recently proposed black bounce geometries, amongst others. We show that these compact objects possess a far richer geometrical structure than their general relativistic counterparts.

We investigate negative tension branes as stable thin shell wormholes in Reissner-Nordström-(anti) de Sitter spacetimes in d dimensional Einstein gravity. Imposing Z₂ symmetry, we construct and classify traversable static thin shell wormholes in spherical, planar (or cylindrical) and hyperbolic symmetries. In spherical geometry, we find the higher dimensional counterpart of Barceló and Visser’s wormholes, which are stable against spherically symmetric perturbations. We also find the classes of thin shell wormholes in planar and hyperbolic symmetries with a negative cosmological constant, which are stable against perturbations preserving symmetries. In most cases, stable wormholes are found with the combination of an electric charge and a negative cosmological constant. However, as special cases, we find stable wormholes even with vanishing cosmological constant in spherical symmetry and with vanishing electric charge in hyperbolic symmetry.