35 research outputs found
Magnetized Anisotropic Dark Energy Bianchi Type III Cosmological Models in Brans-Dicke Theory of Gravitation
We investigate the spatially homogeneous Bianchi Type III cosmological models with magnetized anisotropic dark energy fluid in the scalar tensor theory of gravitation proposed by Brans-Dicke [1]. The solutions of the models are obtained by volumetric exponential expansion, power law expansion and power law relation between scalar field and scale factor ‘a’. The physical aspects of the dark energy models are discussed
Interacting Two Fluid Viscous Dark Energy Cosmological Models in Bianchi Type II Universe
In this paper, we present a class of solutions of Barber’s second self creation field equations describing two fluid models of the universe in locally rotationally symmetric Bianchi type II universe filled with the barotropic fluid and bulk viscous dark energy fluid. Exact solutions of the field equations are obtained for non-interacting and interacting two fluid models. The Physical behavior of the model has been discussed
Bianchi type II models in the presence of perfect fluid and anisotropic dark energy
Spatially homogeneous but totally anisotropic and non-flat Bianchi type II
cosmological model has been studied in general relativity in the presence of
two minimally interacting fluids; a perfect fluid as the matter fluid and a
hypothetical anisotropic fluid as the dark energy fluid. The Einstein's field
equations have been solved by applying two kinematical ans\"{a}tze: we have
assumed the variation law for the mean Hubble parameter that yields a constant
value of deceleration parameter, and one of the components of the shear tensor
has been considered proportional to the mean Hubble parameter. We have
particularly dwelled on the accelerating models with non-divergent expansion
anisotropy as the Universe evolves. Yielding anisotropic pressure, the fluid we
consider in the context of dark energy, can produce results that can be
produced in the presence of isotropic fluid in accordance with the \Lambda CDM
cosmology. However, the derived model gives additional opportunities by being
able to allow kinematics that cannot be produced in the presence of fluids that
yield only isotropic pressure. We have obtained well behaving cases where the
anisotropy of the expansion and the anisotropy of the fluid converge to finite
values (include zero) in the late Universe. We have also showed that although
the metric we consider is totally anisotropic, the anisotropy of the dark
energy is constrained to be axially symmetric, as long as the overall energy
momentum tensor possesses zero shear stress.Comment: 15 pages; 5 figures; matches the version published in The European
Physical Journal Plu
Variable Modified Chaplygin Gas in Anisotropic Universe with Kaluza-Klein Metric
In this work, we have consider Kaluza-Klein Cosmology for anisotropic
universe where the universe is filled with variable modified chaplygin gas
(VMCG). Here we find normal scalar field and the self interacting
potential to describe the VMCG Cosmology. Also we graphically
analyzed the geometrical parameters named {\it statefinder parameters} in
anisotropic Kaluza-Klein model. Next, we consider a Kaluza-Klein model of
interacting VMCG with dark matter in the Einstein gravity framework. Here we
construct the three dimensional autonomous dynamical system of equations for
this interacting model with the assumption that the dark energy and the dark
matter are interact between them and for that we also choose the interaction
term. We convert that interaction terms to its dimensionless form and perform
stability analysis and solve them numerically. We obtain a stable scaling
solution of the equations in Kaluza-Klein model and graphically represent
solutions.Comment: 11 pages, 13 figure
Some anisotropic universes in the presence of imperfect fluid coupling with spatial curvature
We consider Bianchi VI spacetime, which also can be reduced to Bianchi types
VI0-V-III-I. We initially consider the most general form of the energy-momentum
tensor which yields anisotropic stress and heat flow. We then derive an
energy-momentum tensor that couples with the spatial curvature in a way so as
to cancel out the terms that arise due to the spatial curvature in the
evolution equations of the Einstein field equations. We obtain exact solutions
for the universes indefinetly expanding with constant mean deceleration
parameter. The solutions are beriefly discussed for each Bianchi type. The
dynamics of the models and fluid are examined briefly, and the models that can
approach to isotropy are determined. We conclude that even if the observed
universe is almost isotropic, this does not necessarily imply the isotropy of
the fluid (e.g., dark energy) affecting the evolution of the universe within
the context of general relativity.Comment: 17 pages, no figures; to appear in International Journal of
Theoretical Physics; in this version (which is more concise) an equation
added, some references updated and adde
Bianchi Type I Cosmology in Generalized Saez-Ballester Theory via Noether Gauge Symmetry
In this paper, we investigate the generalized Saez-Ballester scalar-tensor
theory of gravity via Noether gauge symmetry (NGS) in the background of Bianchi
type I cosmological spacetime. We start with the Lagrangian of our model and
calculate its gauge symmetries and corresponding invariant quantities. We
obtain the potential function for the scalar field in the exponential form. For
all the symmetries obtained, we determine the gauge functions corresponding to
each gauge symmmetry which include constant and dynamic gauge. We discuss
cosmological implications of our model and show that it is compatible with the
observational data.Comment: 13 pages, 2 figures, accepted for publication in 'European Physical
Journal C
Non-vacuum Solutions of Bianchi Type VI_0 Universe in f(R) Gravity
In this paper, we solve the field equations in metric f(R) gravity for
Bianchi type VI_0 spacetime and discuss evolution of the expanding universe. We
find two types of non-vacuum solutions by taking isotropic and anisotropic
fluids as the source of matter and dark energy. The physical behavior of these
solutions is analyzed and compared in the future evolution with the help of
some physical and geometrical parameters. It is concluded that in the presence
of isotropic fluid, the model has singularity at and represents
continuously expanding shearing universe currently entering into phantom phase.
In anisotropic fluid, the model has no initial singularity and exhibits the
uniform accelerating expansion. However, the spacetime does not achieve
isotropy as in both of these solutions.Comment: 20 pages, 5 figures, accepted for publication in Astrophys. Space Sc
Reconstruction of , and models inspired by variable deceleration parameter
We study an special law for the deceleration parameter, recently proposed by
Akarsu and Dereli, in the context of , and
theories of modified gravity. This law covers the law of Berman for obtaining
exact cosmological models to account for the current acceleration of the
universe, and also gives the opportunity to generalize many of the dark energy
models having better consistency with the cosmological observations. Our aim is
to reconstruct the , and models inspired by this
law of variable deceleration parameter. Such models may then exhibit better
consistency with the cosmological observations.Comment: 18 pages, Published online in Astrophys. Space. Sc
A New Class of Bianchi Type-I Cosmological Models in Scalar-Tensor Theory of Gravitation and Late Time Acceleration
A new class of a spatially homogeneous and anisotropic Bianchi type-I
cosmological models of the universe for perfect fluid distribution within the
framework of scalar-tensor theory of gravitation proposed by Saez and Ballester
(Phys. Lett. 113:467, 1986) is investigated. To prevail the deterministic
solutions we choose the different scale factors which yield time-dependent
deceleration parameters (DP) representing models which generate a transition of
the universe from the early decelerated phase to the recent accelerating phase.
Three different physically viable models of the universe are obtained in which
their anisotropic solutions may enter to some isotropic inflationary era. The
modified Einstein's field equations are solved exactly and the models are found
to be in good concordance with recent observations. Some physical and geometric
properties of the models are also discussed.Comment: 16 pages, 8 figure