It has been argued that the recently detected ring-down gravity waveforms could be indicative only of the presence of light rings in a horizonless object, such as a surgical Schwarzschild wormhole, with the frequencies differing drastically from those of the horizon quasinormal mode frequencies ω QNM at late times. While the possibility of such a horizonless alternative is novel by itself, we show by the example of Ellis-Bronnikov wormhole that the differences in ω QNM in the eikonal limit (large l) need not be drastic. This result will be reached by exploiting the connection between ω QNM and the Bozza strong field lensing parameters. We shall also show that the lensing observables of the EllisBronnikov wormhole can also be very close to those of a black hole (say, SgrA * hosted by our galaxy) of the same mass. This situation indicates that the ringdown frequencies and lensing observables of the Ellis-Bronnikov wormhole can remarkably mimic those of a black hole. The constraint on wormhole parameter γ imposed by experimental accuracy is briefly discussed. We also provide independent arguments supporting the stability of the Ellis-Bronnikov wormhole proven recently.---------------

A basic constraint to be satisfied by Brans class I solution for being a traversible wormhole is derived. It is argued that the solution could be a wormhole analogue of the Horowitz-Ross naked black hole. It is further demonstrated that the wormhole is traversible only "in principle", but not in practice. Using a recently proposed measure of total gravitational energy inside a static wormhole configuration, it is shown that the wormhole contains repulsive gravity required for the defocussing of orbits at the throat. PACS number(s): 04.20. Gz, 04.62.+v

We investigate the strong field lensing observables for the Damour-Solodukhin wormhole and examine how small the values of the deviation parameter λ need be for reproducing the observables for the Schwarzschild black hole. While the extremely tiny values of λ indicated by the matter accretion or Hawking evaporation are not disputed, it turns out that λ could actually assume values considerably higher than those tiny values and still reproduce black hole lensing signatures. The lensing observations thus provide a surprising counterexample to the intuitive expectation that all experiments ought to lead to the mimicking of black holes for the same range of values of λ.

It is concluded in the literature that Ellis wormhole is unstable under small perturbations and would decay either to the Schwarzschild black hole or expand away to infinity. While this deterministic conclusion of instability is correct, we show that the Ellis wormhole reduces to Schwarzschild black hole only when the Ellis solution parameter γ assumes a complex value −i. We shall then reexamine stability of Ellis and phantom wormholes from the viewpoint of local and asymptotic observers by using a completely different approach, viz., we adapt Tangherlini's nondeterministic, prequantal 1 arXiv:1606.04356v1 [gr-qc] 6 Jun 2016 statistical simulation about photon motion in the real optical medium to an effective medium reformulation of motions obtained via Hamilton's opticalmechanical analogy in a gravity field. A crucial component of Tangherlini's idea is the observed increase of momentum of the photons entering a real medium. We show that this fact has a heuristic parallel in the effective medium version of the Pound-Rebka experiment in gravity. Our conclusion is that there is a non-zero probability that Ellis and phantom wormholes could appear stable or unstable depending on the location of observers and on the values of γ, leading to the possibility of ghost wormholes (like ghost stars). The Schwarzschild horizon, however, would always appear certainly stable (R = 1, T = 0) to observers regardless of their location. Phantom wormholes of bounded mass in the extreme limit a → −1 are also shown to be stable just as the Schwarzschild black hole is. We shall propose a thought experiment showing that our non-deterministic results could be numerically translated into observable deterministic signatures of ghost wormholes.

Recently, it has been shown by Lobo, Parsaei and Riazi (LPR) that phantom energy with $\omega =p_{r}/\rho <-1$ could support phantom wormholes. Several classes of such solutions have been derived by them. While the inner spacetime is represented by asymptotically flat phantom wormhole that have repulsive gravity, it is most likely to be unstable to perturbations. Hence, we consider a situation, where a phantom wormhole is somehow trapped inside a Schwarzschild sphere across a thin shell. Applying the method developed by Garcia, Lobo and Visser (GLV), we shall exemplify that the shell can possess zones of stability depending on certain constraints. It turns out that zones corresponding to "force" constraint are more restrictive than those from the "mass" constraint. We shall also enumerate the interior energy content by using the gravitational energy integral proposed by Lynden-Bell, Katz and Bi% \v{c}\'ak. It turns out that, even though the interior mass is positive, the integral implies repulsive energy. This is consistent with the phantom nature of interior matter.Comment: 10 pages, 3 figures, Indian J Phys 201