3,705 research outputs found
Matter power spectrum for the generalized Chaplygin gas model: The relativistic case
The generalized Chaplygin gas (GCG) model is the prototype of a unified model
of dark energy (DE) and dark matter (DM). It is characterized by
equation-of-state (EoS) parameters and . We use a statistical
analysis of the 2dFGRS data to constrain these parameters. In particular, we
find that very small (close to zero) and very large values () of
the equation-of-state parameter are preferred. To test the validity of
this type of unification of the dark sector we admit the existence of a
separate DM component in addition to the Chaplygin gas and calculate the
probability distribution for the fractional contributions of both components to
the total energy density. This analysis favors a model for which the Universe
is nearly entirely made up of the separate DM component with an almost
negligible Chaplygin gas part. This confirms the results of a previous
Newtonian analysis.Comment: Latex file, 8 pages, 15 figures in eps forma
Static, spherically symmetric solutions with a scalar field in Rastall gravity
Rastall's theory belongs to the class of non-conservative theories of
gravity. In vacuum, the only non-trivial static, spherically symmetric solution
is the Schwarzschild one, except in a very special case. When a canonical
scalar field is coupled to the gravity sector in this theory, new exact
solutions appear for some values of the Rastall parameter . Some of these
solutions describe the same space-time geometry as the recently found solutions
in the -essence theory with a power function for the kinetic term of the
scalar field. There is a large class of solutions (in particular, those
describing wormholes and regular black holes) whose geometry coincides with
that of solutions of GR coupled to scalar fields with nontrivial
self-interaction potentials; the form of these potentials, however, depends on
the Rastall parameter . We also note that all solutions of GR with a zero
trace of the energy-momentum tensor, including black-hole and wormhole ones,
may be re-interpreted as solutions of Rastall's theory.Comment: Latex file, 18 pages. To fit published versio
Phantom Black Holes in Einstein-Maxwell-Dilaton Theory
We obtain the general static, spherically symmetric solution for the
Einstein-Maxwell-dilaton system in four dimensions with a phantom coupling for
the dilaton and/or the Maxwell field. This leads to new classes of black hole
solutions, with single or multiple horizons. Using the geodesic equations, we
analyse the corresponding Penrose diagrams revealing, in some cases, new causal
structures.Comment: Latex file, 32 pages, 15 figures in eps format. Typo corrected in Eq.
(3.18
Density perturbations in an Universe dominated by the Chaplygin gas
We study the fate of density perturbations in an Universe dominate by the
Chaplygin gas, which exhibit negative pressure. We show that it is possible to
obtain the value for the density contrast observed in large scale structure of
the Universe by fixing a free parameter in the equation of state of this gas.
The negative character of pressure must be significant only very recently.Comment: Latex file, 5 page
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