共查询到20条相似文献，搜索用时 703 毫秒
1.
R. Chaubey 《Astrophysics and Space Science》2012,342(2):499-509
The Bianchi type-V cosmological model with viscous fluid and creation particle in Brans-Dicke theory has been considered. The present paper deals with Bianchi type-V cosmological model with bulk viscosity and particle creation described by full causal thermodynamics in Brans-Dicke theory. We have discussed two types of solutions of the average scale factor for a Bianchi type-V model by using a variation law of Hubble’s parameter, which yields a constant value of the deceleration parameter. The exact solutions to the corresponding field equations are obtained in quadrature form. The solutions to the Einstein field equations are obtained for power law and exponential form. The cosmological parameters have been discussed in detail. 相似文献
2.
J. P. Singh 《Astrophysics and Space Science》2008,318(1-2):103-107
In this paper, we investigate a variation law for Hubble’s parameter in the curved, expanding background of spatially homogeneous, anisotropic Bianchi type I space-time. By choosing a particular form of the generalized Hubble’s parameter, which gives an early deceleration and late time acceleration for the anisotropic Bianchi type I cosmological model, we show that the model approaches isotropy and tends to a de Sitter universe at late times. The cosmological term asymptotically tends to a genuine cosmological constant and the solution is consistent with recent observations. 相似文献
3.
C. P. Singh 《Astrophysics and Space Science》2009,323(2):197-203
In this paper we consider a locally-rotationally-symmetric (LRS) Bianchi type-V perfect fluid model with variable cosmological
‘constant’ representing the energy density of vacuum. The field equations are solved with and without heat conduction by using
a variation law for the mean Hubble parameter, which is related to the average scale factor of the metric and yields a constant
value of the deceleration parameter. A constant value of deceleration parameter generates power-law form of average scale
factor which is used to find the exact solutions with and without heat conduction with decaying vacuum density. The solutions
presented here satisfy all the necessary conditions for the physically acceptability. The thermodynamical relations in decaying
vacuum fluid model are also studied in detail. 相似文献
4.
We have studied cosmological model generated by perfect fluid coupled with mass less scalar field for Kantowski–Sachs space–time in general theory of relativity. Two different physically viable models of the universe are obtained by using a special law of variation for Hubble’s parameter that yields a constant value of deceleration parameter. Some physical consequences of the models have been discussed in case of Zel’dovich fluid. 相似文献
5.
A special law of variation for Hubble’s parameter is presented in a spatially homogeneous and anisotropic Bianchi type-I space-time
that yields a constant value of deceleration parameter. Using the law of variation for Hubble’s parameter, exact solutions
of Einstein’s field equations are obtained for Bianchi-I space-time filled with perfect fluid in two different cases where
the universe exhibits power-law and exponential expansion. It is found that the solutions are consistent with the recent observations
of type Ia supernovae. A detailed study of physical and kinematical properties of the models is carried out. 相似文献
6.
Sanjay Sarkar 《Astrophysics and Space Science》2014,350(2):821-829
In this work, we have considered the spatially homogeneous and anisotropic Bianchi type-II universe filled with two interacting fluids; dark matter and holographic dark energy components. Assuming the proportionality relation between one of the components of shear scalar and expansion scalar which yields time dependent deceleration parameter, an exact solution to Einstein’s field equations in Bianchi type-II line element is obtained. We have investigated geometric and kinematics properties of the model and the behaviour of the holographic dark energy. It is observed that the mean anisotropic parameter is uniform through the whole evolution of the universe and the coincidence parameter increases with increasing time. The solutions are also found to be in good agreement with the results of recent observations. We have applied the statefinder diagnostics method to study the behaviour of different stages of the universe and to differentiate the proposed dark energy model from the ΛCDM model. We have also established a correspondence between the holographic dark energy model and the tachyon scalar field dark energy model. We have reconstructed the potential and the dynamics of the tachyon scalar field, which describes accelerated expansion of the universe. 相似文献
7.
Sanjay Sarkar 《Astrophysics and Space Science》2014,352(2):859-866
The present work deals with the accretion of two minimally interacting fluids: dark matter and a hypothetical isotropic fluid as the holographic dark energy components onto black hole and wormhole in a spatially homogeneous and anisotropic Bianchi type-V universe. To obtain an exact solution of the Einstein’s field equations, we use the assumption of linearly varying deceleration parameter. Solution describes effectively the actual acceleration and indicates a big rip type future singularity of the universe. We have studied the evolution of the mass of black hole and the wormhole embedded in this anisotropic universe in order to reproduce a stable universe protected against future-time singularity. It is observed that the accretion of these dark components leads to a gradual decrease and increase of black hole and wormhole mass respectively. Finally, we have found that contrary to our previous case (Sarkar in Astrophys. Space. Sci. 341:651, 2014a), the big rip singularity of the universe with a divergent Hubble parameter of this dark energy model may be avoided by a big trip. 相似文献
8.
We utilise a form for the Hubble parameter to generate a number of solutions to the Einstein field equations with variable cosmological constant and variable gravitational constant. The Hubble law utilised yields a constant value for the deceleration parameter. A variety of solutions is presented in the Robertson-Walker spacetimes. A generalisation of the cosmic scale factor is utilised in the anisotropic Bianchi I spacetime to illustrate that new solutions may also be found in spacetimes with less symmetry than Robertson-Walker. We also show that the constant deceleration parameter used is consistent with alternate theories of gravity by considering the scalar-tensor theory of Lau and Prokhovnik with ak = 0 Robertson-Walker background. 相似文献
9.
Sanjay Sarkar 《Astrophysics and Space Science》2014,349(2):985-993
The paper deals with a spatially homogeneous and anisotropic Bianchi type-I universe filled with two minimally interacting fluids; matter and holographic dark energy components. The nature of the holographic dark energy for Bianchi type-I space time is discussed. An exact solution to Einstein’s field equations in Bianchi type-I line element is obtained using the assumption of linearly varying deceleration parameter. Under the suitable condition, it is observed that the anisotropy parameter of the universe approaches to zero for large cosmic time and the coincidence parameter increases with increasing time. We established a correspondence between the holographic dark energy models with the generalised Chaplygin gas dark energy model. We also reconstructed the potential and dynamics of the scalar field which describes the Chaplygin cosmology. Solution of the field equations shows that a big rip type future singularity will occur for this model. It has been observed that the solutions are compatible with the results of recent observations. 相似文献
10.
V. U. M. Rao T. Vinutha M. Vijaya Shanthi G. Sree Devi Kumari 《Astrophysics and Space Science》2008,317(1-2):89-94
Exact Bianchi type-V cosmological models are presented in Einstein’s theory of gravitation with cosmological constant Λ in case of perfect fluid distribution. Also obtained Bianchi type-V cosmological models in a scalar-tensor theory of gravitation proposed by Saez and Ballester (1986) in case of perfect fluid distribution using and without using negative constant deceleration parameter. Some physical and geometrical properties of the models are also discussed. 相似文献
11.
Anirudh Pradhan Rekha Jaiswal Rajeev Kumar Khare 《Astrophysics and Space Science》2013,343(1):489-497
On getting motivation from increasing evidence for the need of a geometry that resembles Bianchi morphology to explain the observed anisotropy in the WMAP data, Einstein’s field equations with variable cosmological “constant” are considered in presence of perfect fluid for a homogeneous and anisotropic Bianchi type-I space-time. Einstein’s field equations are solved by considering a time dependent deceleration parameter which affords a late time acceleration in the universe. The cosmological constant Λ is found to be a decreasing function of time and it approaches a small positive value at the present epoch which is corroborated by consequences from recent supernovae Ia observations. From recently developed Statefinder pair, the behavior of different stages of the evolution of the universe has been studied. The physical significance of the cosmological models have also been discussed. 相似文献
12.
In this paper we have studied the anisotropic and homogeneous Bianchi type-I universe filled with interacting Dark matter and Holographic dark energy. Here we discussed two models, in first model the solutions of the field equations are obtained for constant value of deceleration parameter where as in the second model the solutions of the field equations are obtained for special form of deceleration parameter. It is shown that for suitable choice of interaction between dark matter and holographic dark energy there is no coincidence problem (unlike ΛCDM). Also, in all the resulting models the anisotropy of expansion dies out very quickly and attains isotropy after some finite time. The Statefinder diagnostic is applied to both the models in order to distinguish between our dark energy models with other existing dark energy models. The physical and geometrical aspects of the models are also discussed. 相似文献
13.
In this paper, we have investigated plane symmetric cosmological models with negative constant deceleration parameter in Barber’s (Gen. Relativ. Gravit. 14:117, 1982) second self-creation theory in presence of perfect fluid source. For this we use a special law of variation for Hubble parameter proposed by Bermann (Nuovo Cim. B 74:182, 1983) that yields a constant deceleration parameter model of the universe. Some physical properties of the models and entropy are discussed and studied. 相似文献
14.
We have studied the evolution of homogeneous and anisotropic Bianchi type-I cosmological models filled with perfect fluid
in Barber second self-creation theory by assuming a special law of variation for Hubble’s parameter that yield a constant
value of deceleration parameter. Some physical consequences of the models have been discussed in case of Zel’dovich fluid
and radiation dominated fluid. 相似文献
15.
C. P. Singh 《Astrophysics and Space Science》2011,331(1):337-342
The evolution and dynamics of a locally-rotationally-symmetric (LRS) Bianchi type-V space-time cosmological models are discussed
with variable gravitational and cosmological “constants” in context of the particle creation. We present the exact solutions
of Einstein field equations by using a power-law form of the average scale factor of the metric in the case of the particle
creation and in the absence of particle creation. The solution describes the particle and entropy generation in the anisotropic
cosmological models. The particle creation rate is uniquely determined by the variation of gravitational and cosmological
“constants”. We observe that the variable gravitational constant does not necessarily imply particle creation. In a generic
situation, models can be interpolated between different phases of the universe. The dynamical behaviors of the solutions and
kinematical parameters of the model are discussed in detail. 相似文献
16.
《New Astronomy》2021
This study set out to examine the effect of anisotropy on the various dark energy models by using the observational data, including the Sandage-Loeb test, Strongly gravitationally lensing, observational Hubble data, and Baryon Acoustic Oscillations data. In particular, we consider three cases of dark energy models: the cosmological constant model, which is most favored by current observations, the wCDM model where dark energy is introduced with constant w equation of state parameter and in Chevalier-Polarski-Linder parametrization where ω is allowed to evolve with redshift. With an anisotropy framework, a maximum likelihood method to constrain the cosmological parameters was implemented. With an anisotropic universe, we also study the behavior of different cosmological parameters such as Hubble parameter, EoS parameter, and deceleration parameter of dark energy models mentioned. The results indicate that the Bianchi type I model for the dark energy models are consistent with the combined observational data. 相似文献
17.
The nature of scalar field potentials plays a dominant role in the cosmological dynamics of scalar-tensor gravity. The superpotential reconstruction technique is an interesting way to determine the nature of scalar field potentials by taking the Hubble parameter as a function of scalar field. The present study is an application of this technique in the gravitational framework of scalar-tensor gravity using LRS Bianchi type I universe. We explore the nature of scalar field potentials for some particular cases. It is found that the potentials in all cases turn out to be of polynomial nature and the anisotropy parameter m classifies its degree. The graphical behavior of the directional Hubble parameter shows monotonic behavior which is in contrast to the FRW case. 相似文献
18.
Exact solutions of the field equations for a Bianchi type-I space-time, filled with a viscous fluid and cosmological constant,
are obtained. We utilize the constancy of deceleration parameter to get singular and non-singular solutions. We investigate
a number of solutions with constant and time-varying cosmological constant together with a linear relation between shear viscosity
and expansion scalar. Due to dissipative processes, the mean anisotropy and shear of the model tend to zero at a faster rate. 相似文献
19.
Bianchi type V viscous fluid cosmological model for barotropic fluid distribution with varying cosmological term Λ is investigated. We have examined a cosmological scenario proposing a variation law for Hubble parameter H in the background of homogeneous, anisotropic Bianchi type V space-time. The model isotropizes asymptotically and the presence of shear viscosity accelerates the isotropization. The model describes a unified expansion history of the universe indicating initial decelerating expansion and late time accelerating phase. Cosmological consequences of the model are also discussed. 相似文献
20.
We have studied anisotropic and homogeneous Locally Rotationally Symmetric (LRS) Bianchi type-I, Bianchi type-V, Bianchi type-III, Bianchi type-VI0, and Kantowaski–Sachs space-times with variable equation of state (EoS) parameter (w) in General Relativity. A special form of deceleration parameter (q) which gives an early deceleration and late time accelerating cosmological model has been utilized to solve the field equations. The geometrical and physical aspects of the models are also studied. 相似文献