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1.
In this paper we have obtained some new exact solutions of Einstein’s field equations in a spatially homogeneous and anisotropic
Bianchi type-V space-time with perfect fluid distribution along with heat-conduction and decaying vacuum energy density Λ
by applying the variation law for generalized Hubble’s parameter that yields a constant value of deceleration parameter. We
find that the constant value of deceleration parameter is reasonable for the present day universe. The variation law for Hubble’s
parameter generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential
form. Using these two forms, Einstein’s field equations are solved separately that correspond to expanding singular and non-singular
models of the universe respectively. The cosmological constant Λ is found to be a decreasing function of time and positive
which is corroborated by results from recent supernovae Ia observations. Expressions for look-back time-redshift, neoclassical
tests (proper distance d(z)), luminosity distance red-shift and event horizon are derived and their significance are described in detail. The physical
and geometric properties of spatially homogeneous and anisotropic cosmological models are discussed. 相似文献
2.
Spatially homogeneous and anisotropic LRS Bianchi type-I metric is considered in the framework of Nordtvedt-Barker’s general
scalar-tensor theory of gravitation when the source for the energy momentum tensor is a perfect fluid. With the help of a
special law of variation for Hubble’s parameter proposed by Berman (Nuovo Cim. B. 74:182, 1983) a cosmological model with negative constant deceleration parameter is obtained. Some physical and kinematical properties
of the model are also discussed. 相似文献
3.
J. P. Singh 《International Journal of Theoretical Physics》2009,48(7):2041-2049
In the present paper, we investigate the possibility of a variation law for Hubble’s parameter H in the background of spatially homogeneous, anisotropic Bianchi type V space-time with perfect fluid source and time-dependent
cosmological term. The model obtained presents a cosmological scenario which describes an early deceleration and late time
acceleration. The model approaches isotropy and tends to a de Sitter universe at late times. The cosmological term Λ asymptotically
tends to a genuine cosmological constant. It is observed that the solution is consistent with the results of recent observations. 相似文献
4.
5.
Lallan Yadav Vineet K. Yadav T. Singh 《International Journal of Theoretical Physics》2012,51(10):3113-3126
The present paper envisages a spatially homogeneous and anisotropic Bianchi II massive string cosmological models with time-decaying Λ term in general relativity. By using the variation law of Hubble’s parameter, the Einstein’s field equations have been solved for two general cases. The first case involving a power law solution describes the dynamics of universe from big bang to present epoch while the second case admit an exponential solution seems reasonable to project dynamics of future universe. We observed that massive strings dominate in early universe and eventually disappear at late time, which is consistent with the current astronomical observations. It has been found that the cosmological constant (Λ) is a decreasing function of time and it approaches to small positive value at sufficiently large time. The thermodynamic properties of anisotropic Bianchi II universe are studied and also the absolute temperature and entropy distribution are given explicitly. The relations between thermodynamic parameters and cosmological constant Λ has been established. Physical behavior of the derived model is elaborated in detail. 相似文献
6.
V. U. M. Rao M. Vijaya Santhi T. Vinutha G. Sree?Devi?Kumari 《International Journal of Theoretical Physics》2012,51(10):3303-3310
Bianchi type-I dark energy model with variable equation of state (EoS) parameter is presented in a scalar-tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124:925, 1961). To get a determinate solution of the field equations we will take the help of special law of variation for Hubble’s parameter presented by Bermann (Nuovo Cimento B. 74:182, 1983) which yields a dark energy cosmological model with negative constant deceleration parameter. It is observed that this dark energy cosmological model always represents an accelerated and expanding universe and also consistent with the recent observations of type-Ia supernovae. Some physical and geometrical properties of the model are also discussed. 相似文献
7.
C. P. Singh Mohd Zeyauddin Shri Ram 《International Journal of Theoretical Physics》2008,47(12):3162-3170
The variation law for generalized mean Hubble’s parameter is discussed in a spatially homogeneous and anisotropic Bianchi
type V space-time with perfect fluid along with heat-conduction. The variation law for Hubble’s parameter, that yields a constant
value of deceleration parameter, generates two types of solutions for the average scale factor, one is of power-law type and
other one of exponential form. Using these two forms of the average scale factor, exact solutions of Einstein field equations
with a perfect fluid and heat conduction are presented for a Bianchi type V space-time, which represent expanding singular
and non-singular cosmological models. We find that the constant value of deceleration parameter is reasonable for the present
day universe. The physical and geometrical properties of the models are also discussed in detail. 相似文献
8.
We propose a new law for the deceleration parameter that varies linearly with time and covers Berman’s law where it is constant.
Our law not only allows one to generalize many exact solutions that were obtained assuming constant deceleration parameter,
but also gives a better fit with data (from SNIa, BAO and CMB), particularly concerning the late time behavior of the universe.
According to our law only the spatially closed and flat universes are allowed; in both cases the cosmological fluid we obtain
exhibits quintom like behavior and the universe ends with a big-rip. This is a result consistent with recent cosmological
observations. 相似文献
9.
We consider Einstein’s field equations with variable gravitational and cosmological “constants” for a spatially homogeneous
and anisotropic Bianchi-I space-time. A law of variation for the Hubble parameter, which is related to the average scale factor
and yields a constant value of the deceleration parameter, is assumed to solve the field equations. The gravitational constant
is allowed to follow a power-law form. We find that a time-increasing gravitational constant is suitable for describing the
present evolution of universe. The solutions reveal the dynamics of a universe, which expands forever. The physical interpretation
of the solutions is discussed in detail. 相似文献
10.
P C Vaidya 《Pramana》1984,22(3-4):151-158
In addition to the Kerr metric with cosmological constant Λ several other metrics are presented giving a Kerr-like solution
of Einstein’s equations in the background of deSitter universe. A new metric of what may be termed as rotating deSitter space-time—a
space-time devoid of matter but containing null fluid with twisting null rays, has been presented. This metric reduces to
the standard deSitter metric when the twist in the rays vanishes. Kerr metric in this background is the immediate generalization
of Schwarzschild’s exterior metric with cosmological constant. 相似文献
11.
Kanti Jotania Padminin Yadav S. A. Faruqi 《International Journal of Theoretical Physics》2011,50(5):1424-1443
The present study deals with a spatially homogeneous and anisotropic Bianchi-II cosmological models representing massive strings
by applying the variation law for generalized Hubble’s parameter that yields a constant value of deceleration parameter. We
find that the constant value of deceleration parameter is reasonable for the present day universe. The variation law for Hubble’s
parameter generates two types of solutions for the average scale factor, one is of power-law type and other is of the exponential
form. Using these two forms, Einstein’s field equations are solved separately that correspond to expanding singular and non-singular
models of the universe respectively. The energy-momentum tensor for such string as formulated by Letelier (Phys. Rev. D 28:2414,
1983) is used to construct massive string cosmological models for which we assume that the expansion (θ) in the model is proportional to the component s11\sigma^{1}_{1} of the shear tensor sji\sigma^{j}_{i}. This condition leads to A=(BC)
m
, where A, B and C are the metric coefficients and m is proportionality constant. Our models are in accelerating phase which is consistent to the recent observations. The cosmological
constant Λ is found to be a decreasing function of time and it approaches a small positive value at present epoch which is
in good agreement by the results from recent supernovae observations. Some physical and geometric behaviour of the models
are also discussed. 相似文献
12.
Anisotropic Bianchi Type-I cosmological models have been studied on the basis of Lyra’s geometry. Two types of models, one
with constant deceleration parameter and the other with variable deceleration parameter have been derived by considering a
time-dependent displacement field. 相似文献
13.
K. S. Adhav A. S. Nimkar M. R. Ugale M. V. Dawande 《International Journal of Theoretical Physics》2008,47(3):634-639
Bianchi type-III space time is considered in the presence of perfect fluid source in the scalar-tensor theory of gravitation
proposed by Brans and Dicke (Phys. Rev. 124:925, 1961). With the help of special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento 74B:182, 1983) a cosmological model with negative constant deceleration parameter is obtained in the presence of perfect fluid with disordered
radiation. Some physical and kinematical properties of the model are also discussed. 相似文献
14.
D. R. K. Reddy R. L. Naidu B. Satyanarayana 《International Journal of Theoretical Physics》2012,51(10):3045-3051
An axially symmetric Bianchi type-I space time with variable equation of state (EoS) parameter and constant deceleration parameter has been investigated in scale covariant theory of gravitation formulated by Canuto et al. (Phys. Rev. Lett. 39:429, 1977). With the help of special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento 74B:182, 1983) a dark energy cosmological model is obtained in this theory. Some physical and kinematical properties of the model are also discussed. 相似文献
15.
The present study deals with a spatially homogeneous and anisotropic Bianchi type-I (B-I) cosmological models representing
massive strings in normal gauge for Lyra’s manifold by applying the variation law for generalized Hubble’s parameter that
yields a constant value of deceleration parameter. The variation law for Hubble’s parameter generates two types of solutions
for the average scale factor, one is of power-law type and other is of the exponential-law type. Using these two forms, Einstein’s
modified field equations are solved separately that correspond to expanding singular and non-singular models of the universe
respectively. The energy-momentum tensor for such string as formulated by Letelier, P.S.: Phys. Rev. D 28, 2414 (1983) is used to construct massive string cosmological models for which we assume that the expansion (θ) in the model is proportional to the component s1 1\sigma^{1}_{~1} of the shear tensor sj i\sigma^{j}_{~i}. This condition leads to A=(BC)
m
, where A, B and C are the metric coefficients and m is proportionality constant. Our models are in accelerating phase which is consistent to
the recent observations. It has been found that the displacement vector β behaves like cosmological term Λ in the normal gauge treatment and the solutions are consistent with recent observations
of SNe Ia. It has been found that massive strings dominate in the both decelerating and accelerating universes. The strings
dominate in the early universe and eventually disappear from the universe for sufficiently large times. This is in consistent
with the current observations. Some physical and geometric behaviour of these models are also discussed. 相似文献
16.
The cosmological constant problem is examined within the context of the covariant brane-world gravity, based on Nash’s embedding
theorem for Riemannian geometries. We show that the vacuum structure of the brane-world is more complex than General Relativity’s
because it involves extrinsic elements, in specific, the extrinsic curvature. In other words, the shape (or local curvature)
of an object becomes a relative concept, instead of the “absolute shape” of General Relativity. We point out that the immediate
consequence is that the cosmological constant and the energy density of the vacuum quantum fluctuations have different physical
meanings: while the vacuum energy density remains confined to the four-dimensional brane-world, the cosmological constant
is a property of the bulk’s gravitational field that leads to the conclusion that these quantities cannot be compared, as
it is usually done in General Relativity. Instead, the vacuum energy density contributes to the extrinsic curvature, which
in turn generates Nash’s perturbation of the gravitational field. On the other hand, the cosmological constant problem ceases
to be in the brane-world geometry, reappearing only in the limit where the extrinsic curvature vanishes. 相似文献
17.
FRW models have been studied in the cosmological theory based on Lyra’s geometry. A new class of exact solutions has been
obtained by considering a time dependent displacement field for constant deceleration parameter models of the universe.
Dedicated to Professor V B Johri on his sixtieth birthday. 相似文献
18.
The problems of non-static plane symmetric meson field and mesonic perfect fluid in Rosen’s [Gen. Rel. Grav., Vol. 4 (1973)
435] bimetric theory of gravitation are considered. It is observed that plane symmetric non-static cosmological model exists
in case of scalar meson field where the scalar field becomes constant. Further it is found that in case of mesonic perfect
fluid, the bimetric theory does not admit perfect fluid but allows only mesonic scalar field with constant scalar field. In
both the cases a cosmological model with constant scalar field is obtained. 相似文献
19.
Dipanjali Behera Sunil K. Tripathy Tushar R. Routray 《International Journal of Theoretical Physics》2010,49(10):2569-2581
Bulk Viscous anisotropic Bianchi-III cosmological models are investigated with time dependent gravitational and cosmological
constants in the framework of Einstein’s general relativity. In order to get some useful information about the time varying
nature of G and Λ, we have assumed an exponentially decaying rest energy density of the universe. The extracted Newtonian gravitational
constant G varies with time but its time varying nature depends on bulk viscosity and the anisotropic nature of the model. The cosmological
constant Λ is found to decrease with time to a small but positive value for the models. 相似文献
20.
A class of new LRS Bianchi type-I cosmological models with a variable cosmological term is investigated in presence of perfect
fluid. A procedure to generate new exact solutions to Einstein’s field equations is applied to LRS Bianchi type-I space-time.
Starting from some known solutions a class of new perfect fluid solutions of LRS Bianchi type-I are obtained. The cosmological
constant Λ is found to be positive and a decreasing function of time which is supported by results from recent supernovae Ia observations.
The physical and geometric properties of spatially homogeneous and anisotropic cosmological models are discussed. 相似文献