768 research outputs found
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
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
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
Maxwell equations in homogeneous spaces with solvable groups of motions
The classification of exact solutions of Maxwell vacuum equations for the
case when the electromagnetic fields and metrics of homogeneous spaces are
invariant with respect to the motion group G(VII) is completed. All
non-equivalent exact solutions of Maxwell vacuum equations for electromagnetic
fields and spaces with such symmetry have been obtained. The vectors of the
canonical frame of a homogeneous space of type VII according to the Bianchi
classification, and the electromagnetic field potentials have been found.Comment: 10 pages. arXiv admin note: text overlap with arXiv:2204.0703
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