228 research outputs found
Linearized stability of charged thin-shell wormholes
The linearized stability of charged thin shell wormholes under spherically
symmetric perturbations is analized. It is shown that the presence of a large
value of charge provides stabilization to the system, in the sense that the
constrains onto the equation of state are less severe than for non-charged
wormholes.Comment: 8 pages, 2 figures; v2: minor changes. Accepted for publication in
General Relativity and Gravitatio
Thin-shell wormholes from charged black holes in generalized dilaton-axion gravity
This paper discusses a new type of thin-shell wormhole constructed by
applying the cut-and-paste technique to two copies of a charged black hole in
generalized dilaton-axion gravity, which was inspired by low-energy string
theory. After analyzing various aspects of this thin-shell wormhole, we discuss
its stability to linearized spherically symmetric perturbations.Comment: Minor changes, 6 pages, 4 figures. Accepted for publication in Gen.
Rel. Gra
A Theoretical Construction of Thin Shell Wormhole from Tidal Charged Black hole
Recently, Dadhich et al [ Phys.Lett.B 487, 1 (2000)] have discovered a black
hole solution localized on a three brane in five dimensional gravity in the
Randall-Sundrum scenario. In this article, we develop a new class of thin shell
wormhole by surgically grafting above two black hole spacetimes. Various
aspects of this thin wormhole are also analyzed.Comment: 14 pages, 6 figures, Accepted in Gen.Rel.Gra
Gravitational microlensing of gamma-ray blazars
We present a detailed study of the effects of gravitational microlensing on
compact and distant -ray blazars. These objects have -ray
emitting regions which are small enough as to be affected by microlensing
effects produced by stars lying in intermediate galaxies. We analyze the
temporal evolution of the gamma-ray magnification for sources moving in a
caustic pattern field, where the combined effects of thousands of stars are
taken into account using a numerical technique. We propose that some of the
unidentified -ray sources (particularly some of those lying at high
galactic latitude whose gamma-ray statistical properties are very similar to
detected -ray blazars) are indeed the result of gravitational lensing
magnification of background undetected Active Galactic Nuclei (AGNs).Comment: 30 pages, 27 figures. Four figures are being submitted only as .gif
files, and should be printed separately. The abstract below has been
shortened from the actual version appearing in the pape
On the possibility of an astronomical detection of chromaticity effects in microlensing by wormhole-like objects
We study the colour changes induced by blending in a wormhole-like
microlensing scenario with extended sources. The results are compared with
those obtained for limb darkening. We assess the possibility of an actual
detection of the colour curve using the difference image analysis method.Comment: Accepted for publication in Modern Physics Letters A. 13 report
pages, 7 figure
Chromaticity effects in microlensing by wormholes
Chromaticity effects introduced by the finite source size in microlensing
events by presumed natural wormholes are studied. It is shown that these
effects provide a specific signature that allow to discriminate between
ordinary and negative mass lenses through the spectral analysis of the
microlensing events. Both galactic and extragalactic situations are discussed.Comment: To appear in Modern Physics Letters A, 200
Thin-shell wormholes from regular charged black holes
We investigate a new thin-shell wormhole constructed by surgically grafting
two regular charged black holes arising from the action using nonlinear
electrodynamics coupled to general relativity. The stress-energy components
within the shell violate the null and weak energy conditions but obey the
strong energy condition. We study the stability in two ways: (i) taking a
specific equation of state at the throat and (ii) analyzing the stability to
linearized spherically symmetric perturbations about a static equilibrium
solution. Various other aspects of this thin-shell wormhole are also analyzed.Comment: 8 pages and 19 figure
Gravitational lensing as a possible explanation for some unidentified gamma-ray sources at high latitudes
We propose that some of the high-latitude unidentified EGRET gamma-ray
sources could be the result of gravitational lensing amplification of the
innermost regions of distant, faint, active galactic nuclei. These objects have
gamma-ray emitting regions small enough as to be affected by microlensing of
stars in interposed galaxies. We compute the gravitational amplification taking
into account effects of the host galaxy of the lens and prove that, whereas the
innermost gamma-ray regions can be magnified up to thousand times, there is no
amplification at radio frequencies, leading to the observed absence of strong
counterparts. Some new effects in the spectral evolution of a gravitational
microlensed gamma-ray AGN are predicted. Within a reasonable range of lensing
parameters, and/or types of sources, both variable and non-variable EGRET
detections at high latitudes can be explained by microlensing. The same
phenomenon could also have an important incidence among the future GLAST
detections at high-latitudes.Comment: Accepted for publication in The Astrophysical Journal. Scheduled to
appear in April, 2002. 2 figure
Rotating thin-shell wormhole from glued Kerr spacetimes
We construct a model of a rotating wormhole made by cutting and pasting two
Kerr spacetimes. As a result, we obtain a rotating thin-shell wormhole with
exotic matter at the throat. Two candidates for the exotic matter are
considered: (i) a perfect fluid; (ii) an anisotropic fluid. We show that a
perfect fluid is unable to support a rotating thin-shall wormhole. On the
contrary, the anisotropic fluid with the negative energy density can be a
source for such a geometry.Comment: 8 pages, 3 figures, accepted for publication in Gravitation and
Cosmolog
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