243 research outputs found
Specially Coupled Dark Energy in the Oscillating FRW Cosmology
We consider a four-dimensional flat-space Friedman universe, which is filled
with two interacting ideal fluids (the coupling of dark energy with dark matter
of special form). The gravitational equations of motion are solved. It is shown
that in some cases there appears a periodic universe with finite-time
cosmological singularities and also the universe becomes static in the remote
future.Comment: 4 page
Little Rip and Pseudo Rip Phenomena from Coupled Dark Energy
We consider Little Rip (LR) and Pseudo Rip (PR) cosmological models with two
interacting ideal fluids, corresponding to dark energy and dark matter. The
interaction between the dark energy and the dark matter fluid components is
described in terms of the parameters in the equations of state for the LR and
PR universes. In contrast to a model containing only a pure dark energy, the
presence of the interaction term between the fluid components in the
gravitational equations leads to a modification of the equation of state
parameters. The properties of the early universe in this formalism are pointed
out.Comment: 11 pages, Latex2e, no figures. To appear in Modern Physics Letters
Inhomogeneous viscous dark fluid coupled with dark matter in the FRW universe
A cosmological model with an inhomogeneous viscous dark fluid coupled with
dark matter in a flat Friedman-Robertson-Walker universe is investigated. The
influence of dark matter on the behavior of an inhomogeneous viscous fluid of
this kind, responsible for cosmic acceleration and for the appearance of
different types of singularities, is analyzed in detail. In particular, the
critical points corresponding to the solutions of the background equations in a
useful approximation are obtained explicitly.Comment: 11 pages, 2 figures, to appear in MPL
Inflation in Terms of a Viscous van der Waals Coupled Fluid
We propose to describe the acceleration of the universe by introducing a
model of two coupled fluids. We focus on the accelerated expansion at the early
stages. The inflationary expansion is described in terms of a van der Waals
equation of state for the cosmic fluid, when account is taken of bulk
viscosity. We assume that there is a weak interaction between the van der Waals
fluid and the second component (matter). The gravitational equations for the
energy densities of the two components are solved for a homogeneous and
isotropic Friedmann-Robertson-Walker universe, and analytic expressions for the
Hubble parameter are obtained. The slow-roll parameters, the spectral index,
and the tensor-to-scalar ratio are calculated and compared with the most recent
astronomical data from the Planck satellite. Given reasonable restriction on
the parameters, the agreement with observations is favorable.Comment: 7 pages, no figures. To appear in Int. J. Geom. Meth. Mod. Phy
Rip Cosmology via Inhomogeneous Fluid
The conditions for the appearance of the Little Rip, Pseudo Rip and Quasi Rip
universes in the terms of the parameters in the equation of state of some dark
fluid are investigated. Several examples of the Rip cosmologies are
investigated.Comment: 107-11
- …