242 research outputs found
Chaplygin electron gas model
We provide a new electromagnetic mass model admitting Chaplygin gas equation
of state. We investigate three specializations, the first characterized by a
vanishing effective pressure, the second provided with a constant effective
density and the third is described by a constant effective pressure. For these
specializations two particular cases are discussed. In addition, for
specialization I, case I we found isotropic coordinate as well as Kretschmann
scalar, and for specialization III, case II two special scenarios have been
studied.Comment: LaTex, some typos correcte
Generalized Chaplygin Gas Models tested with SNIa
The so called Generalized Chaplygin Gas (GCG) with the equation of state was recently proposed as a candidate for dark
energy in the Universe. In this paper we confront the GCG with SNIa data.
Specifically we have tested the GCG cosmology in three different classes of
models with (1) , ; (2) ,
and (3) , , as well as the
model withouth any assumption on . The best fitted models are
obtained by minimalizing the function and levels in the
plane. We supplemented our analysis with confidence intervals
in the plane, as well as one-dimensional probability
distribution functions for models parameter. The general conclusion is that
SNIa data strongly support the Chaplygin gas (with ). Extending our
analysisby relaxing the flat prior lead to the result that even though the best
fitted values of are formally non-zero, still they are close to flat
case. It should be viewed as an advantage of the GCG model since in similar
analysisof CDM model high negative value of were found to
be bestfitted to the data and independent inspiration from CMBR and
extragalactic astronomy has been invoked to fix the curvature problem. Our
results show clearly that in Generalized Chaplygin Gas cosmology distant
supernovae should be brighter than in CDM model.This prediction seems
to be confirmed with new Riess high redshift SNIa sample. Moreover, we argue
that with the future SNAP data it would be possible to differentiate between
models with various value of parameter and/or discriminated between
GCG, Cardassian and CDM modelsComment: 54 pages 29 figures improved version analysis flat prior relaxed high
redshift Riess SNIa sample include
Some new class of Chaplygin Wormholes
Some new class of Chaplygin wormholes are investigated in the framework of a
Chaplygin gas with equation of state , . Since
empty spacetime () does not follow Chaplygin gas, so the
interior Chaplygin wormhole solutions will never asymptotically flat. For this
reason, we have to match our interior wormhole solution with an exterior vacuum
solution i.e. Schwarzschild solution at some junction interface, say .
We also discuss the total amount of matter characterized by Chaplygin gas that
supplies fuel to construct a wormhole.Comment: 14 pages, 12 figures, Accepted for publication in Mod.Phys.Lett.
On the motion of a heavy rigid body in an ideal fluid with circulation
Chaplygin's equations describing the planar motion of a rigid body in an
unbounded volume of an ideal fluid involved in a circular flow around the body
are considered. Hamiltonian structures, new integrable cases, and partial
solutions are revealed, and their stability is examined. The problems of
non-integrability of the equations of motion because of a chaotic behavior of
the system are discussed.Comment: 25 pages, 4 figure
Traversable wormholes in a string cloud
We study spherically symmetric thin-shell wormholes in a string cloud
background in (3+1)-dimensional spacetime. The amount of exotic matter required
for the construction, the traversability and the stability under radial
perturbations, are analyzed as functions of the parameters of the model.
Besides, in the Appendices a non perturbative approach to the dynamics and a
possible extension of the analysis to a related model are briefly discussed.Comment: 21 pages, 10 figures; accepted for publication in Int. J. Mod. Phys.
Dilaton thin-shell wormholes supported by a generalized Chaplygin gas
In this article, we construct spherical thin-shell wormholes with charge in
dilaton gravity. The exotic matter required for the construction is provided by
a generalized Chaplygin gas. We study the stability under perturbations
preserving the symmetry. We find that the increase of the coupling between the
dilaton and the electromagnetic fields reduces the range of the parameters for
which stable configurations are possible.Comment: 14 pages, 6 figures. v3: typos correcte
Gravitationally Collapsing Shells in (2+1) Dimensions
We study gravitationally collapsing models of pressureless dust, fluids with
pressure, and the generalized Chaplygin gas (GCG) shell in (2+1)-dimensional
spacetimes. Various collapse scenarios are investigated under a variety of the
background configurations such as anti-de Sitter(AdS) black hole, de Sitter
(dS) space, flat and AdS space with a conical deficit. As with the case of a
disk of dust, we find that the collapse of a dust shell coincides with the
Oppenheimer-Snyder type collapse to a black hole provided the initial density
is sufficiently large. We also find -- for all types of shell -- that collapse
to a naked singularity is possible under a broad variety of initial conditions.
For shells with pressure this singularity can occur for a finite radius of the
shell. We also find that GCG shells exhibit diverse collapse scenarios, which
can be easily demonstrated by an effective potential analysis.Comment: 27 pages, Latex, 11 figures, typos corrected, references added, minor
amendments in introduction and conclusion introd
Dynamics of the Tippe Top -- properties of numerical solutions versus the dynamical equations
We study the relationship between numerical solutions for inverting Tippe Top
and the structure of the dynamical equations. The numerical solutions confirm
oscillatory behaviour of the inclination angle for the symmetry
axis of the Tippe Top. They also reveal further fine features of the dynamics
of inverting solutions defining the time of inversion. These features are
partially understood on the basis of the underlying dynamical equations
Modified Chaplygin Traversable Wormholes
The modified Chaplygin gas (MCG) is a strong candidate for the unified model
of dark matter and dark energy. The equation of state of this modified model is
valid from the radiation era to the CDM model. In early epoch (when
was large), dark matter had the dominant role while at later stages
(when is small), the MCG model behaves as dark energy. In this work, we
have found exact solution of static spherically symmetric Einstein equations
describing a wormhole for an inhomogeneous distribution of modified Chaplygin
gas. For existence of wormhole solution, there are some restrictions relating
the parameters in the equation of state for MCG and the throat radius of the
wormhole. Physical properties and characteristics of these modified Chaplygin
wormholes are analyzed in details.Comment: 9 pages, 1 figur
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