Kidderpore College

We propose a novel way to regularize the JNW globally naked singularity, which is sourced by the canonical Einstein minimally coupled scalar field (EMS). The key idea is to complexify (Wick rotate) the JNW parameters, this yields a regular metric that surprisingly represents a twice asymptotically flat regular traversable wormhole, famously known as the Ellis class III wormhole sourced by the ghost EMS. We begin by arguing that the JNW solution belongs to a hierarchy of actions describing different gravity theories, which indicates that a regularized version of JNW automatically provides corresponding regular versions of the solution within the hierarchy of these gravity theories.

In a recent article, Hod (Eur Phys J C 80:982, 2020) has concluded the non-existence, heretofore unnoticed, of a unified Thorne’s hoop conjecture that holds for the quasi-local mass, ℳ(r≤ R_+) for static Reissner–Nordstrőm black hole, but does not hold for the spinning electrically charged Kerr–Newman black holes, when the same quasi-local mass is used. While the conclusion is correct and important, we wish to point out a curious exception for which the conjecture holds in a unified way for both the static and spinning tidal charged 4d braneworld black holes of string theory, when the mass in the conjecture is the same quasi-local mass.

Asymptotic zero Arnowitt-Deser-Misner (ADM) mass wormholes, such as the zero-mass traversable Ellis-Bronnikov wormhole, are of great interest for astrophysical applications such as in the galactic microlensing. However, when considered individually, they are unstable to small perturbations. On the other hand, there is a possibility that they can be stable as an interior partner of a traversable glued wormhole obtained by suitably gluing the interior to the observationally relevant massive exterior spacetimes across spherically symmetric thin shells. Although the exterior spacetime has non-zero ADM mass, massless interior partner remains massless sharing the stability of the glued wormhole. The dynamics of the thin-shell then demarcates the stability regions of the glued wormhole that we wish to study here by employing the novel concepts of thin-shell "mass" and of "external force" constraints discovered by Garcia, Lobo and Visser. We shall consider two classes, where the zero ADM mass interior are Kim-Lee wormholes glued to the exterior Schwarzschild vacuum and Reissner-Nordström spacetime respectively. It turns out that the stability regions in both cases are almost similar although the two interior Kim-Lee spacetimes are physically very different, one scalar charged and the other electrically charged. The conditions under which the stability of glued wormholes could be achieved are analyzed in detail.

In this paper it is decided to derive the strong field lensing observables for black hole foils which is considered as the Damour-Solodukhin wormhole and also to examine the range of the deviation parameter λ for which it mimics Schwarzschild black holes in both the classical and quantum level. The lensing observables for the black hole SgrA^* residing in our galaxy can be interpreted to provide a numerical expression of ∼10^-3 .

The authors study the Sagnac effect in the space-time of a spinning black hole with tidal charge β. It is shown that the strongest influence of the tidal (electric) charge is observed close to the black hole. An increase in the tidal charge lengthens the Sagnac delay. Numerical estimates show that the Sagnac delay for the Earth is determined in the range of –63.8 to –1.5 ns.