61 research outputs found
The Wahlquist metric cannot describe an isolated rotating body
It is proven that the Wahlquist perfect fluid space-time cannot be smoothly
joined to an exterior asymptotically flat vacuum region. The proof uses a power
series expansion in the angular velocity, to a precision of the second order.
In this approximation, the Wahlquist metric is a special case of the rotating
Whittaker space-time. The exterior vacuum domain is treated in a like manner.
We compute the conditions of matching at the possible boundary surface in both
the interior and the vacuum domain. The conditions for matching the induced
metrics and the extrinsic curvatures are mutually contradictory.Comment: 13 pages, 0 figure
Traversable Wormholes Construction in 2+1 Dimensions
We study traversable Lorentzian wormholes in the three-dimensional low energy
string theory by adding some matter source involving a dilaton field. It will
be shown that there are two-different types of wormhole solutions such as BTZ
and black string wormholes depending on the dilaton backgrounds, respectively.
We finally obtain the desirable solutions which confine exotic matter near the
throat of wormhole by adjusting NS charge.Comment: 12 pages, 4 figures, JHEP style, one reference adde
Petrov types of slowly rotating fluid balls
Circularly rotating axisymmetric perfect fluid space-times are investigated
to second order in the small angular velocity. The conditions of various
special Petrov types are solved in a comoving tetrad formalism. A number of
theorems are stated on the possible Petrov types of various fluid models. It is
shown that Petrov type II solutions must reduce to the de Sitter spacetime in
the static limit. Two space-times with a physically satisfactory
energy-momentum tensor are investigated in detail. For the rotating
incompressible fluid, it is proven that the Petrov type cannot be D. The
equation of the rotation function can be solved for the Tolman type
IV fluid in terms of quadratures. It is also shown that the rotating version of
the Tolman IV space-time cannot be Petrov type D.Comment: 14 pages, version to appear in Gen. Rel. Gra
Relativistic Compact Objects in Isotropic Coordinates
We present a matrix method for obtaining new classes of exact solutions for
Einstein's equations representing static perfect fluid spheres. By means of a
matrix transformation, we reduce Einstein's equations to two independent
Riccati type differential equations for which three classes of solutions are
obtained. One class of the solutions corresponding to the linear barotropic
type fluid with an equation of state is discussed in detail.Comment: 9 pages, no figures, accepted for publication in Pramana-Journal of
Physic
Phantom Wormholes in (2+1)-dimensions
In this paper, we have constructed a (2+1)-dimensional wormhole using
inhomogeneous and anisotropic distribution of phantom energy. We have
determined the exact form of the equation of state of phantom energy that
supports the wormhole structure. Interestingly, this equation of state is
linear but variable one and is dependent only on the radial parameter of the
model.Comment: 10 pages, 5 figure
Linearized stability analysis of thin-shell wormholes with a cosmological constant
Spherically symmetric thin-shell wormholes in the presence of a cosmological
constant are constructed applying the cut-and-paste technique implemented by
Visser. Using the Darmois-Israel formalism the surface stresses, which are
concentrated at the wormhole throat, are determined. This construction allows
one to apply a dynamical analysis to the throat, considering linearized radial
perturbations around static solutions. For a large positive cosmological
constant, i.e., for the Schwarzschild-de Sitter solution, the region of
stability is significantly increased, relatively to the null cosmological
constant case, analyzed by Poisson and Visser. With a negative cosmological
constant, i.e., the Schwarzschild-anti de Sitter solution, the region of
stability is decreased. In particular, considering static solutions with a
generic cosmological constant, the weak and dominant energy conditions are
violated, while for the null and strong energy conditions are
satisfied. The surface pressure of the static solution is strictly positive for
the Schwarzschild and Schwarzschild-anti de Sitter spacetimes, but takes
negative values, assuming a surface tension in the Schwarzschild-de Sitter
solution, for high values of the cosmological constant and the wormhole throat
radius.Comment: 16 pages, 10 figures, LaTeX2e, IOP style files. Accepted for
publication in Classical and Quantum Gravit
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