44 research outputs found
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
Vacuumless topological defects in Lyra geometry
Few years ago, Cho and Vilenkin have proposed that topological defects can
arise in symmetry breaking models without having degenerate vacua. These types
of defects are known as vacuumless defects. In the present work, the
gravitational field of a vacuumless global string and global monopole have been
investigated in the context of Lyra geometry. We find the metric of the
vacuumless global string and global monopole in the weak field approximations.
It has been shown that the vacuumless global string can have repulsive whereas
global monopole exerts attractive gravitational effects on a test particle. It
is dissimilar to the case studied in general relativity.Comment: 14 pages, 9 figures. To appear in Astrophys.Space.Sc
Gravitational field of domain wall in Lyra geometry
In this paper, we study the domain wall with time dependent displacement
vectors based on Lyra geometry in normal gauge i.e. displacement vector . The field theoretic energy momentum tensor is
considered with zero pressure perpendicular to the wall. We find an exact
solutions of Einstein equation for a scalar field with a potential
describing the gravitational field of a plane symmetric domain wall.
We have seen that the hyper surfaces parallel to the wall ()
are three dimensional de-sitter spaces. It is also shown that the gravitational
field experienced by test particle is attractive.Comment: 11 pages, 6 figures; Submitted in Astrophysics and Space Science
after minor revisio
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
Accelerating Bianchi Type-V Cosmology with Perfect Fluid and Heat Flow in Saez-Ballester Theory
In this paper we discuss the law of variation of scale factor which yields a time-dependent deceleration
parameter (DP) representing a new class of models that generate a transition of
universe from the early decelerated phase to the recent accelerating phase.
Exact solutions of Einstein's modified field equations with perfect fluid and
heat conduction are obtained within the framework of Saez-Ballester
scalar-tensor theory of gravitation and the model is found to be in good
agreement with recent observations. We find, for n = 3, k = 1, the present
value of DP in derived model as q_0 = -0.67 which is very near to the observed
value of DP at present epoch. We find that the time-dependent DP is sensible
for the present day Universe and give an earmark description of evolution of
universe. Some physical and geometric properties of the models are also
discussed.Comment: 12 pages, 5 figure
Statefinder Parameters for Different Dark Energy Models with Variable G Correction in Kaluza-Klein Cosmology
In this work, we have calculated the deceleration parameter, statefinder
parameters and EoS parameters for different dark energy models with variable
correction in homogeneous, isotropic and non-flat universe for Kaluza-Klein
Cosmology. The statefinder parameters have been obtained in terms of some
observable parameters like dimensionless density parameter, EoS parameter and
Hubble parameter for holographic dark energy, new agegraphic dark energy and
generalized Chaplygin gas models.Comment: 9 pages, no figure, accepted for publication in IJTP. arXiv admin
note: text overlap with arXiv:1104.2366 by other author
Bianchi type-II modified holographic Ricci dark energy cosmological model in the presence of massive scalar field
Non-vacuum plane symmetric universe in f(R) gravity
In this paper, we investigate a non-static plane symmetric model in the presence of perfect fluid distribution in f(R) theory of gravity. Here R is the Ricci scalar of the space-time. We have derived, explicitly, the field equations of this theory. We have obtained a determinate solution of the field equations using (i) the shear scalar σ of the space-time is proportional to expansion scalar θ which leads to a relation between metric potentials, and (ii) a power law between the scalaron function F of the theory and average scale factor a(t) of the universe. The solution obtained represents an implicit exponential model of the universe with a variable deceleration parameter. This is a unique feature of our model which is different from other models obtained assuming time varying deceleration parameter. We have found the cosmological parameters, namely, pressure, energy density, spatial volume, mean Hubble’s parameter, shear, average anisotropy and expansion scalars of our model which are significant in the discussion of cosmology. We have discussed their physical significance through graphical representation. It is observed that the deceleration parameter exhibits a smooth transition from early deceleration to late time acceleration of the universe. It is also observed that our model satisfies the null energy condition. Keywords: Non-static plane symmetric metric, Perfect fluid, f(R) gravity, Modified gravity, Accelerating mode