共查询到20条相似文献，搜索用时 19 毫秒
1.
Hypersurface–homogeneous cosmological models containing a bulk viscous fluid with time varying G and Λ have been presented. We have shown that the field equations are solvable for any arbitrary cosmic scale function. The
viscosity coefficient of bulk viscous fluid is assumed to be a power function of the energy density. Exact solutions of Einstein’s
field equations are obtained which represent an expanding, shearing and accelerating/decelerating models of the universe.
The physical and kinematical behaviours of the models are also discussed. 相似文献
2.
Bulk viscous cosmological models of universe with variable deceleration parameter in Lyra’s Manifold
N. Ibotombi Singh S. Romaleima Devi S. Surendra Singh A. Sumati Devi 《Astrophysics and Space Science》2009,321(3-4):233-239
FRW models of universe in the presence of viscous fluid are investigated in the cosmological theory based on Lyra’s Manifold. By considering the deceleration parameter to be a variable and the viscosity coefficient of bulk viscous fluid to be a constant, exacts solutions have been obtained from which three forms of model of the universe are derived. The physical properties of the models are also investigated. 相似文献
3.
T. Vidyasagar C. Purnachandra Rao R. Bhuvana Vijaya D. R. K. Reddy 《Astrophysics and Space Science》2014,349(1):467-471
A spatially homogeneous and anisotropic Bianchi type-III space-time is considered in the presence of bulk viscous fluid containing one dimensional cosmic strings in the frame work of a scalar-tensor theory of gravity proposed by Saez and Ballester (in Phys. Lett. A 113:467, 1986). We have obtained a determinate solution of the field equations of this theory, using (i) a barotropic equation of state for the pressure and density and (ii) the bulk viscous pressure is proportional to the energy density. Some physical properties of the model are also discussed. 相似文献
4.
A spatially homogeneous and anisotropic Bianchi type-III space-time is considered in the presence of bulk viscous fluid containing one dimensional cosmic strings in the frame work of f(R,T) gravity proposed by Harko et al. (Phys. Rev. D 84:024020, 2011). To get a determinate solution of the field equations of this theory, we have used (i) a barotropic equation of state for the pressure and density and (ii) the bulk viscous pressure is proportional to the energy density. It is interesting to observe that, in this case, Bianchi type-III bulk viscous string cosmological model does not exist and degenerates into vacuum model of general relativity. 相似文献
5.
Nawsad Ali 《Journal of Astrophysics and Astronomy》2013,34(3):259-271
The present study deals with spatially homogeneous and anisotropic axially symmetric Bianchi type-I cosmological model with time variable cosmological term Λ in the presence of bulk viscous fluid. The Einstein’s field equations are solved explicitly by time varying deceleration parameter q. Consequences of the four cases of phenomenological decay of Λ have been discussed which are consistent with observations. Physical and kinematical parameters of the models are discussed. 相似文献
6.
A spatially homogeneous and anisotropic Bianchi type-V space–time is considered in the frame work of a scale covariant theory of gravitation proposed by Canuto et al. (Phys. Rev. Lett. 39:429, 1977) when the matter sources is a bulk viscous fluid containing one dimensional cosmic strings. Using some physically plausible conditions, we have obtained a determinate solution of the field equations of the theory which represents a Bianchi type-V bulk viscous string cosmological model in this theory. Some physical and kinematical properties of the model are also discussed. 相似文献
7.
T. Vidya Sagar C. Purnachandra Rao R. Bhuvana Vijaya D. R. K. Reddy 《Astrophysics and Space Science》2014,349(1):479-483
A spatially homogeneous and anisotropic Bianchi type-III space-time is considered in the framework of a scalar-tensor theory of gravitation proposed by Brans and Dicke (Phys. Rev. 124:925, 1961) in the presence of bulk viscous fluid containing one dimensional cosmic strings. We have found a determinate solution of the field equations using the plausible physical conditions (i) a barotropic equation state for the pressure and density, (ii) special law of variation for Hubble’s parameter proposed by Berman (Nuovo Cimento B74:182, 1983), (iii) shear scalar is proportional to scalar expansion and (iv) the trace of the energy tensor of the fluid vanishes. We have also assumed that bulk viscous pressure is proportional to energy density. Some physical and kinematical properties of the model are, also, discussed. 相似文献
8.
Bianchi Type-V bulk viscous fluid string dust cosmological model in General Relativity is investigated. It has been shown
that if coefficient of bulk viscosity (ζ) is inversely proportional to the expansion (θ) in the model then string cosmological
model for Bianchi Type-V space-time is possible. In absence of bulk viscosity (ζ), i.e. when ζ → 0, then there is no string
cosmological model for Bianchi Type-V space-time. The physical and geometrical aspects of the model are also discussed. 相似文献
9.
Sunil K. Tripathy Subodha K. Nayak Subrat K. Sahu Tushar R. Routray 《Astrophysics and Space Science》2009,323(3):281-287
Spatially homogeneous and anisotropic LRSBianchi type-I string cosmological models are studied in the frame work of general relativity when the source for the energy momentum tensor is a bulk viscous fluid containing one dimensional strings embedded in a magnetic field. A barotropic equation of state for the pressure and density is assumed to get determinate solutions of the field equations. The bulk viscous pressure is assumed to be proportional to the energy density. The effects of viscosity and electromagnetic field on the properties of the model are investigated. The role of bulk viscosity and electromagnetic field in getting an inflationary phase and in establishing a string phase in the universe is studied. 相似文献
10.
An exact cosmological solution for Friedman Robertson Walker (FRW)metric is obtained with a classical scalar field φ along
with a potential in the presence of a causal viscous fluid. Assuming the scale factor to be a function of the scalar field
we have obtained solutions in both the truncated and the full causal theory. It is shown that an inflationary model can be
obtained by imposing certain constraints on some constants. The radiative bulk viscosity during the decoupling era has also
been studied as a special case.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
11.
An LRS Bianchi Type V bulk viscous fluid dust distribution string cosmological model in General Relativity is investigated.
It has been shown that if coefficient of bulk viscosity (ζ) is proportional to the expansion (θ) in the model then string
cosmological model for Bianchi Type V space-time is possible. In absence of bulk viscosity(ζ) i.e. when ζ → 0 then there is
no string cosmological model for Bianchi Type V space-time. The physical and geometrical aspects are also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
12.
Many have speculated about the presence of a stiff fluid in very early stage of the universe. Such a stiff fluid was first introduced by Zel’dovich. Recently the late acceleration of the universe was studied by taking bulk viscous stiff fluid as the dominant cosmic component, but the age predicted by such a model is less than the observed value. We consider a flat universe with viscous stiff fluid and decaying vacuum energy as the cosmic components and found that the model predicts a reasonable background evolution of the universe with de Sitter epoch as end phase of expansion. More over, the model also predicts a reasonable value for the age of the present universe. We also performed a dynamical system analysis of the model and found that the end de Sitter phase predicted by the model is stable. 相似文献
13.
The problem of electromagnetic field interacting with viscous fluid without and with zero-mass scalar field has been studied. It has been shown that electromagnetic field cannot interact with viscous fluid for spherically-symmetric Robertson-Walker metric. Exact solutions corresponding to the problem of electromagnetic field interactions in presence of viscous fluid and zero-mass scalar field have been obtained subject to various physical conditions. It presents a scope for the study of imperfect fluid FRW models showing the existence of the electromagnetic field due to the presence of zero-mass scalar field. 相似文献
14.
The paper considers inhomogeneous space-times admitting a two-parameter group of motions and satisfying Einstein's field equations for viscous fluid and perfect fluid with heat conduction. Some homogenous solutions representing viscous fluid have also been obtained for which the free-gravitational field is of the magnetic type. Various physical and kinematical properties have been discussed. 相似文献
15.
D. R. K. Reddy M. P. V. V. Bhaskara Rao K. Sobhan Babu 《Astrophysics and Space Science》2014,351(1):385-389
A spatially homogeneous and anisotropic LRS Bianchi type-II space-time is considered in the frame work of second self-creation theory of gravitation proposed by Barber (Gen. Relativ. Gravit. 14:117, 1982) in the presence of bulk viscous fluid containing one dimensional cosmic strings. A determinate solution of the field equations is presented using special variation for Hubble’s parameter given by Berman (Nuovo Cimento B 74:182, 1983) and some physically plausible conditions. The solution represents a bulk viscous string model in the second self-creation cosmology. We have also discussed some physical and kinematical properties of the model. 相似文献
16.
D. R. K. Reddy R. L. Naidu T. Ramprasd K. V. Ramana 《Astrophysics and Space Science》2013,348(1):241-245
A locally rotationally symmetric(LRS) Bianchi type-II space-time is considered in the frame work of a modified theory of gravitation proposed by Canuto et al. (Phys. Rev. Lett. 39:429, 1977) when the source for energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. A special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento B 74:182, 1983) is used to obtain determinate solution of the field equations. We have also used the barotropic equation of state and the bulk viscous pressure is assumed to be proportional to the energy density. The physical and kinematical properties of the model are also discussed. 相似文献
17.
D. R. K. Reddy R. L. Naidu K. Dasu Naidu T. Ram Prasad 《Astrophysics and Space Science》2013,346(1):219-223
A locally rotationally symmetric (LRS) Bianchi type-II space-time is considered in the frame work of a modified theory of gravitation proposed by Harko et al. (Phys. Rev. D 84:024020, 2011) when the source for energy momentum tensor is a bulk viscous fluid containing one dimensional cosmic strings. A barotropic equation of state is assumed to get a determinate solution of the field equations. Also, the bulk viscous pressure is assumed to be proportional to the energy density. The physical behavior of the model is also discussed. 相似文献
18.
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
19.
Sunil Kumar Tripathy Dipanjali Behera Tushar Ranjan Routray 《Astrophysics and Space Science》2010,325(1):93-97
Spatially homogeneous and anisotropic LRS Bianchi type-I string cosmological models are studied in the frame work of general
relativity when the source for the energy momentum tensor is a bulk viscous fluid containing one dimensional strings. A barotropic
equation of state for the pressure and density is assumed to get determinate solutions of the field equations. The bulk viscous
pressure is assumed to be proportional to the energy density. The physical and kinematical properties of the models are discussed.
The role of bulk viscosity in getting an inflationary phase in the universe is studied. 相似文献
20.
Field equations are obtained in the scalar–tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986) with the aid of spatially homogenous and anisotropic Kantowski–Sachs space–time in the presence of bulk viscous fluid containing one dimensional cosmic strings. A determinate solution of the field equations is obtained, using some plausible physical conditions, which represents a Kantowski–Sach’s bulk viscous Cosmological model in the new scalar–tensor theory. Physical and kinematical properties of the model are also discussed. 相似文献