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.
We extend a recent work on weak field first order light deflection in the MOdified Gravity (MOG) by comprehensively analyzing the actual observables in gravitational lensing both in the weak and strong field regime. The static spherically symmetric black hole (BH) obtained by Moffat is what we call here the Schwarzschild-MOG (abbreviated as SMOG) containing repulsive Yukawa-like force characterized by the MOG parameter α > 0 diminishing gravitational attraction. We point out a remarkable feature of SMOG, viz., it resembles a regular brane-world BH in the range −1 < α < 0 giving rise to a negative "tidal charge" Q (= 1 4 α 1+α ) interpreted as an imprint from the 5D bulk with an imaginary source charge q in the brane. The Yukawa-like force of MOG is attractive in the brane-world range enhancing gravitational attraction. For −∞ < α < −1, the SMOG represents a naked singularity. Specifically, we shall investigate the effect of α or Yukawa-type forces on the weak (up to third PPN order) and strong field lensing observables. For illustration, we consider the supermassive BH SgrA* with α = 0.055 for the weak field to quantify the deviation of observables from GR but in general we leave α unrestricted both in sign and magnitude so that future accurate lensing measurements, which are quite challenging, may constrain α. * Electronic address: izmailov.ramil@gmail.com † Electronic address: karimov ramis 92@mail.ru ‡ Electronic address: zhdanov@ufanet.ru § Electronic address: kamalnandi1952@yahoo.co.in Recent works [1,13,14,23] have motivated us to comprehensively look into the SMOG from another angle, viz., the weak and strong field lensing phenomena that are fundamentally different from each other. The purpose was
Recent trend of research indicates that not only massive but also massless (asymptotic Newtonian mass zero) wormholes can reproduce post-merger initial ring-down gravitational waves characteristic of black hole horizon. In the massless case, it is the non-zero charge of other fields, equivalent to what we call here the "Wheelerian mass", that is responsible for mimicking ring-down quasi-normal modes. In this paper, we enquire whether the same Wheelerian mass can reproduce black hole observables also in an altogether different experiment, viz., the strong field lensing. We examine two classes of massless wormholes, one in the Einstein-Maxwell-Dilaton (EMD) theory and the other in the Einstein-Minimally-coupled-Scalar field (EMS) theory. The observables such as the radius of the shadow, image separation and magnification of the corresponding Wheelerian masses are compared with those of a black hole (idealized SgrA* chosen for illustration) assuming that the three types of lenses share the same minimum impact parameter and distance from the observer. It turns out that, while the massless EMS wormholes can closely mimic the black hole in terms of strong field lensing observables, the EMD wormholes show considerable differences due to the presence of dilatonic charge. The conclusion is that masslessless alone is enough to closely mimic Schwarzschild black hole strong lensing observables in the EMS theory but not in the other, where extra parameters also influence those observables. The motion of timelike particles is briefly discussed for completeness. * Electronic address: izmailov.ramil@gmail.com † Electronic address: zhdanov@ufanet.ru ‡ Electronic address: amrita˙852003@yahoo.co.in § Electronic address: potapovaa2008@rambler.ru ¶ Electronic address: kamalnandi1952@yahoo.co.in 1 It should be mentioned here that Ellis [7] derived two classes of asymptotically flat solutions, one showing naked singularity and the other a regular massive traversable wormhole, which we call here the massive Ellis-Bronnikov wormhole since Bronnikov [8] independently derived it [see the metric (42-45) below]. Interestingly, the two Ellis classes are not really independent but can be connected by a complex Wick rotation, as shown in [9].
Molecular dynamics methods have been used to investigate the kinetics of the liquid-gas phase transition in a two-component Lennard-Jones system at negative pressures and elastic stretches of the liquid to values close to spinodal ones. The molecular dynamics system consists of 2048 interacting particles with parameters of the Lennard-Jones potential for argon and neon. Density dependences of pressure and internal energy have been calculated for stable and metastable states of the mixture at a temperature T* approximately 0.7+/-0.01 and three values of the concentration. The location of mechanical and the diffusion spinodals has been determined. It has been established that a gas-saturated mixture retains its stability against finite variations of state variables up to stretches close to the values near the diffusion spinodal. The statistic laws of the process of destruction of the metastable state have been investigated. The lifetimes of the metastable phase have been determined. It is shown that owing to the small height of the potential barrier that separates the microheterogeneous from the homogeneous state a system of finite size has a possibility to make the reverse transition from the microheterogeneous into the homogeneous state. The lifetimes of the system in the microheterogeneous state, as well as the expectation times of the occurrence of a critical nucleus, are described by Poissonian distributions.
The spinning regular black hole (spin a) metric proposed by Johannsen shares the Kerr horizon but contains independent dimensionless parameters marking deviation from the Kerr metric. Non-zero value of any of the parameters would indicate violation of the no-hair theorem. We shall find the influence of these parameters on the relative time delay (not Shapiro time delay) treated here as a diagnostic for no-hair theorem using aligned, finite, thinlens approximation in realistic spinning astrophysical configurations. Precise measurement of this delay would then help us determine, from observational perspective, whether or not any of the parameters is really non-zero. We shall also point out that the aligned spinning lens is completely equivalent to a "static" lens with a fictitious lens geometry, which would enable us to re-express the relative time delay components in terms of the spin a. Numerical values are tabulated for three astrophysical lens systems. The advantage of the present treatment is that it can accommodate a variety of spinning lens systems that are likely to be detected in the near future.
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