765 research outputs found
Some LRS Bianchi-I String Cosmological Models with Variable Deceleration Parameter
The present study deals with LRS Bianchi type I cosmological model
representing massive string. The energy-momentum tensor for such string as
formulated by Letelier (1983) is used to construct massive string cosmological
models for which we assume that the shear scalar () is proportional to
the expansion scalar (). The study reveals that massive strings
dominate the early Universe. The strings eventually disappear from the Universe
for sufficiently large time, which is in agreement with the current
astronomical observations. Some physical and geometrical behaviour of models
are also discussed.Comment: 11 pages, 6 figures, Unlike the previous version the new one contains
the variable D
Anisotropic massive strings in scalar-tensor theory of gravitation
We present the model of anisotropic universe with string fluid as source of
matter within the framework of scalar-tensor theory of gravitation. Exact
solution of field equations are obtained by applying Berman's law of variation
of Hubble's parameter which yields a constant value of DP. The nature of
classical potential is examined for the model under consideration. It has been
also found that the massive strings dominate in early universe and at long last
disappear from universe. This is in agreement with current astronomical
observations. The physical and dynamical properties of model are also
discussed.Comment: 12 pages, 5 figur
Generation of Bianchi Type V String Cosmological Models with Bulk Viscosity
Bianchi type V string cosmological models with bulk viscosity for massive
string are investigated. The bulk viscosity is assumed to vary with time in
such a manner that it is related to simple power function of the energy
density. Using generation technique (Camci~et~al., 2001), it is shown that
Einstein's field equations are solvable for any arbitrary cosmic scale
function. Solution for particular form of cosmic scale functions are also
obtained. It is found that solutions based on generation technique are relevant
to the observational results. Some physical and geometrical aspect of the
models are also discussed.Comment: 12 pages, 3 figures, Typose removed, To appear in Rom. Rep. Physic
Lyra's cosmology of inhomogeneous universe with electromagnetic field
The plane-symmetric inhomogeneous cosmological models of perfect fluid
distribution with electro-magnetic field is obtained in the framework of Lyra's
geometry. To get the deterministic solution, I have considered , and , where A, B and C are metric
coefficients. It has been found that the solutions generalize the solution
obtained by Pradhan, Yadav and Singh (2007) and are consistent with the recent
observations of type Ia supernovae. A detailed study of physical and
kinematical properties of the models have been carried out.Comment: 25 pages, 2 figure
Bianchi-V string cosmology with power law expansion in Gravity
In this paper, we search the existence of Bianchi-V string cosmological model
in gravity with power law expansion. Einstein's field equations have
been solved by taking into account the law of variation of Hubble's parameter
that yields the constant value of deceleration parameter (DP). We observe that
the massive strings dominate the early universe but they do not survive for
long time and finally disappear from the universe. We examine the nature of
classical potential and also discuss the physical properties of universe.Comment: 6 pages, 4 figure
A transitioning universe with anisotropic dark energy
In this paper, we present a model of transitioning universe with minimal
interaction between perfect fluid and anisotropic dark energy in Bianchi I
space-time. The two sources are assumed to minimally interacted and therefore
their energy momentum tensors are conserved separately. The explicit expression
for average scale factor are considered in hybrid form that gives time varying
deceleration parameter which describes both the early and late time physical
features of universe. We also discuss the physical and geometrical properties
of the model derived in this paper. The solution is interesting physically as
it explain accelerating universe as well as singularity free universe.Comment: 7 pages, 2 figure panel
Bianchi Type V String Cosmological Models in General Relativity
Bianchi type V string cosmological models in general relativity are
investigated. To get the exact solution of Einstein's field equations, we have
taken some scale transformations followed by Camci (2001). It is
shown that Einstein's field equations are solvable for any arbitrary cosmic
scale function. Solution for particular form of cosmic scale functions are also
obtained. Some physical and geometrical aspects of the models are discussed.Comment: 12 pages, Accepted version in Pramana - J. Physic
LRS Bianchi-I Anisotropic Cosmological Model with Dominance of Dark Energy
The present study deals with spatially homogeneous and anisotropic locally
rotationally symmetric (LRS) Bianchi type I cosmological model with dominance
of dark energy. To get the deterministic model of Universe, we assume that the
shear scalar in the model is proportional to expansion scalar
. This condition leads to , where ,\; are metric
potential and is positive constant. It has been found that the anisotropic
distribution of dark energy leads to the present accelerated expansion of
Universe. The physical behavior of the Universe has been discussed in detail.Comment: 11 pages, 4 figures, Accepted for publication in Astrophysics and
Space Scienc
Symmetry Group Analysis for perfect fluid Inhomogeneous Cosmological Models in General Relativity
In this paper, we have searched the existence of the similarity solution for
plane symmetric inhomogeneous cosmological models in general relativity. The
matter source consists of perfect fluid with proportionality relation between
expansion scalar and shear scalar. The isovector fields of Einstein's field
equation for the models under consideration are derived. A new class of exact
solutions of Einstein's field equation have been obtained for inhomogeneous
space-time. The physical behaviors and geometric aspects of the derived models
have been discussed in detail.Comment: 13 page
An optimal system and invariant solutions of dark energy Models in cylindrically symmetric space-time
In this paper, we derive some new invariant solutions of dark energy models
in cylindrically symmetric space-time. To quantify the deviation of pressure
from isotropy, we introduce three different time dependent skewness parameters
along the spatial directions. The matter source consists of dark energy which
is minimally interact with perfect fluid. We use symmetry analysis method for
solving the non-linear partial differential equations (NLPDEs) which is more
powerful than the classical methods of solving NLPDEs. The geometrical and
kinematical features of the models and the behaviour of the anisotropy of dark
energy, are examined in detail.Comment: 13 page
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