83 research outputs found
Stable Gravastars of Anisotropic Dark Energy
Dynamical models of prototype gravastars made of phantom energy are
constructed, in which an infinitely thin spherical shell of a perfect fluid
with the equation of state divides the whole spacetime
into two regions, the internal region filled with a dark energy (or phantom)
fluid, and the external Schwarzschild region. It is found that in some cases
the models represent the "bounded excursion" stable gravastars, where the thin
shell is oscillating between two finite radii, while in other cases they
collapse until the formation of black holes or normal stars. In the phase
space, the region for the "bounded excursion" gravastars is very small in
comparison to that of black holes, but not empty, as found in our previous
papers. Therefore, although the existence of gravastars can not be completely
excluded from current analysis, the opposite is not possible either, that is,
even if gravastars exist, they do not exclude the existence of black holes.Comment: 35 pages, 43 figures, added some clarifying texts and corrected some
typos, accepted for publication in JCA
A single model of traversable wormholes supported by generalized phantom energy or Chaplygin gas
This paper discusses a new variable equation of state parameter leading to
exact solutions of the Einstein field equations describing traversable
wormholes. In addition to generalizing the notion of phantom energy, the
equation of state generates a mathematical model that combines the generalized
phantom energy and the generalized Chaplygin gas models.Comment: 6 pages, no figure
Energy conditions, traversable wormholes and dust shells
Firstly, we review the pointwise and averaged energy conditions, the quantum
inequality and the notion of the ``volume integral quantifier'', which provides
a measure of the ``total amount'' of energy condition violating matter.
Secondly, we present a specific metric of a spherically symmetric traversable
wormhole in the presence of a generic cosmological constant, verifying that the
null and the averaged null energy conditions are violated, as was to be
expected. Thirdly, a pressureless dust shell is constructed around the interior
wormhole spacetime by matching the latter geometry to a unique vacuum exterior
solution. In order to further minimize the usage of exotic matter, we then find
regions where the surface energy density is positive, thereby satisfying all of
the energy conditions at the junction surface. An equation governing the
behavior of the radial pressure across the junction surface is also deduced.
Lastly, taking advantage of the construction, specific dimensions of the
wormhole, namely, the throat radius and the junction interface radius, and
estimates of the total traversal time and maximum velocity of an observer
journeying through the wormhole, are also found by imposing the traversability
conditions.Comment: 11 pages, 3 figures, Revtex
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
Boundary sources in the Doran - Lobo - Crawford spacetime
We take a null hypersurface (the causal horizon) generated by a congruence of
null geodesics as the boundary of the Doran-Lobo-Crawford spacetime, to be the
place where the Brown-York quasilocal energy is located. The components of the
outer and inner stress tensors are computed and shown to depend on time and on
the impact parameter of the test particle trajectory. The surface energy
density on the boundary is given by the same expression as that
obtained previously for the energy stored on a Rindler horizon.Comment: 4 pages, title changed, no figures, minor text change
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
Thin-shell wormholes from black holes with dilaton and monopole fields
We provide a new type of thin-shell wormhole from the black holes with
dilaton and monopole fields. The dilaton and monopole that built the black
holes may supply fuel to construct the wormholes. Several characteristics of
this thin-shell wormhole have been discussed. Finally, we discuss the stability
of the thin-shell wormholes with a "phantom-like" equation of state for the
exotic matter at the throat.Comment: 6 pages and 3 figures, some typos are corrected and accepted in
Int.J.Theor.Phy
Can a wormhole generate electromagnetic field?
We have considered the possibility of a slowly rotating wormhole surrounded
by a cloud of charged particles. Due to slow rotation of the wormhole, the
charged particles are dragged thereby producing an electromagnetic field. We
have determined the strength of this electromagnetic field and the
corresponding flux of radiation.Comment: 9 pages, typos fixe
Stability of Non-asymptotically flat thin-shell wormholes in generalized dilaton-axion gravity
We construct a new type of thin-shell wormhole for non-asymptotically flat
charged black holes in generalized dilaton-axion gravity inspired by low-energy
string theory using cut-and-paste technique. We have shown that this thin shell
wormhole is stable. The most striking feature of our model is that the total
amount of exotic matter needed to support the wormhole can be reduced as
desired with the suitable choice of the value of a parameter. Various other
aspects of thin-shell wormhole are also analyzed.Comment: 15 pages and 11 figures. Minor revisions have been done. Accepted in
Int.J.Theor.Phy
Thin-shell wormholes in Einstein-Maxwell theory with a Gauss-Bonnet term
We study five dimensional thin-shell wormholes in Einstein-Maxwell theory
with a Gauss-Bonnet term. The linearized stability under radial perturbations
and the amount of exotic matter are analyzed as a function of the parameters of
the model. We find that the inclusion of the quadratic correction substantially
widens the range of possible stable configurations, and besides it allows for a
reduction of the exotic matter required to construct the wormholes.Comment: 13 pages, 6 figures; v2: minor changes and new references added.
Accepted for publication in General Relativity and Gravitatio
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