32 research outputs found
Interacting quintessence and the coincidence problem
We investigate the role of a possible coupling of dark matter and dark
energy. In particular, we explore the consequences of such an interaction for
the coincidence problem, i.e., for the question, why the energy densities of
dark matter and dark energy are of the same order just at the present epoch. We
demonstrate, that, with the help of a suitable coupling, it is possible to
reproduce any scaling solution , where is the
scale factor of the Robertson-Walker metric and is a constant parameter.
and are the densities of dark energy and dark matter,
respectively. Furthermore, we show that an interaction between dark matter and
dark energy can drive the transition from an early matter dominated era to a
phase of accelerated expansion with a stable, stationary ratio of the energy
densities of both components.Comment: 3 pages, contribution to the Tenth Marcel Grossmann Meeting, Rio de
Janeiro, 20-26 July 200
New cosmological solutions and stability analysis in full extended thermodynamics
The Einstein's field equations of FRW universes filled with a dissipative
fluid described by full theory of causal transport equations are analyzed. New
exact solutions are found using a non-local transformations on the nonlinear
differential equation for the Hubble factor. The stability of the de Sitter and
asymptotically friedmannian solutions are analyzed using Lyapunov function
method.Comment: 13 pages, LaTeX 2.09. To be published in International Journal of
Modern Physics
Quadratic reheating
The reheating process for the inflationary scenario is investigated
phenomenologically. The decay of the oscillating massive inflaton field into
light bosons is modeled after an out of equilibrium mixture of interacting
fluids within the framework of irreversible thermodynamics. Self-consistent,
analytic results for the evolution of the main macroscopic magnitudes like
temperature and particle number densities are obtained. The models for linear
and quadratic decay rates are investigated in the quasiperfect regime. The
linear model is shown to reheat very slowly while the quadratic one is shown to
yield explosive particle and entropy production. The maximum reheating
temperature is reached much faster and its magnitude is comparable with the
inflaton mass.Comment: 21 pages, LaTeX 2.09, 4 figures. To be published in International
Journal of Modern Physics
Reply to "On scaling solutions with a dissipative fluid"
In this paper we show that the claims in [Class. Quantum Grav. 19 (2002)
3067, gr-qc/0203081] related to our analysis in [Phys. Rev. D 62, 063508
(2000), astro-ph/0005070] are wrong.Comment: 4 pages, uses RevTeX. v2: To appear in Class. Quantum Gra
Cosmological solutions with nonlinear bulk viscosity
A recently proposed nonlinear transport equation is used to model bulk
viscous cosmologies that may be far from equilibrium, as happens during viscous
fluid inflation or during reheating. The asymptotic stability of the de Sitter
and Friedmann solutions is investigated. The former is stable for bulk
viscosity index . New solutions are obtained in
the weakly nonlinear regime for . These solutions are singular and some of
them represent a late-time inflationary era.Comment: 16 pages Latex (IOP style); to appear Class. Quantum Gra
Dissipative cosmological solutions
The exact general solution to the Einstein equations in a homogeneous
Universe with a full causal viscous fluid source for the bulk viscosity index
is found. We have investigated the asymptotic stability of Friedmann
and de Sitter solutions, the former is stable for and the latter for
. The comparison with results of the truncated theory is made. For
, it was found that families of solutions with extrema no longer remain
in the full case, and they are replaced by asymptotically Minkowski evolutions.
These solutions are monotonic.Comment: 17 pages, LaTeX 2.09, 1 figure. To be published in Classical and
Quantum Gravit
Stability of inflationary solutions driven by a changing dissipative fluid
In this paper the second Lyapunov method is used to study the stability of
the de Sitter phase of cosmic expansion when the source of the gravitational
field is a viscous fluid. Different inflationary scenarios related with
reheating and decay of mini-blackholes into radiation are investigated using an
effective fluid described by time--varying thermodynamical quantities.Comment: 17 pages, LaTeX 2.09, 2 figures. To be published in Classical and
Quantum Gravit
Inhomogeneous cosmologies with Q-matter and varying
Starting from the inhomogeneous shear--free Nariai metric we show, by solving
the Einstein--Klein--Gordon field equations, how a self--interacting scalar
field plus a material fluid, a variable cosmological term and a heat flux can
drive the universe to its currently observed state of homogeneous accelerated
expansion. A quintessence scenario where power-law inflation takes place for a
string-motivated potential in the late--time dominated field regime is
proposed.Comment: 11 pages, Revtex. To be published in Physical Review