共查询到20条相似文献,搜索用时 15 毫秒
1.
Five dimensional Kaluza-Klein space-time is considered in the presence of cosmic string source in the frame work of scalar-tensor
theory of gravitation proposed by Saez and Ballester (Phys. Lett. A
113, 467 (1985)). Exact cosmological models, which represent Nambu, Takabayasi and Reddy strings are presented. Some physical
and kinematical properties of the models are also discussed. 相似文献
2.
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
3.
S. K. Tripathy S. K. Nayak S. K. Sahu T. R. Routray 《Astrophysics and Space Science》2009,321(3-4):247-252
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 stiff fluid containing one dimensional strings embedded in electromagnetic field. The bulk viscosity is assumed to be inversely proportional to the scalar expansion. The physical and kinematical properties of the models are discussed. The effects of Viscosity and electromagnetic field on the physical and kinematical properties are also investigated. 相似文献
4.
Mahesh Kumar Yadav Anirudh Pradhan Sheel Kumar Singh 《Astrophysics and Space Science》2007,311(4):423-429
Some Bianchi type-I viscous fluid string cosmological models with magnetic field are investigated. The viscosity coefficient
of bulk viscous fluid is assumed to be a power function of mass density ξ(t)=ξ
0
ρ
m
, where ξ
0 and m are constants. To get a determinate model, we assume conditions ρ=(1+ω)λ, where ρ is rest energy density, ω a positive constant and λ the string tension density and expansion θ is proportional to eigen value σ
11 of the shear tensor σ
j
i
. The behaviour of the models from physical and geometrical aspects in presence and absence of magnetic field is discussed.
相似文献
5.
Five-dimensional spherically symmetric space-time is considered in bimetric theory of gravitation formulated by Rosen (Gen.
Rel. Grav. 4, 435, 1973) in the presence of cosmic string dust cloud. Exact cosmological models which represent geometric (Nambu) string, p-string
(Takabayasi string) and Reddy string (Astrophys. Space Sci. 301, 2006) are obtained in the static and non-static cases. Some physical properties of the models are also discussed. 相似文献
6.
String cloud cosmological models are studied using spatially homogeneous and anisotropic Bianchi type VIh metric in the frame work of general relativity. The field equations are solved for massive string cloud in presence of bulk
viscosity. A general linear equation of state of the cosmic string tension density with the proper energy density of the universe
is considered. The physical and kinematical properties of the models have been discussed in detail and the limits of the anisotropic
parameter responsible for different phases of the universe are explored. 相似文献
7.
An exact Bianchi type-V cosmological model is obtained in a scalar-tensor theory of gravitation proposed by Saez and Ballester
(Phys. Lett. A 113:467, 1986) in case of perfect fluid distribution. Some physical properties of the model are also discussed. 相似文献
8.
《New Astronomy》2021
In this communication, we studied the aspects of bulk viscous fluid cosmological model with quadratic equation of state in the presence of strings loaded with particles in a higher dimensional (5- dimensional) Bianchi type-III geometry in Lyra’s Manifold (Lyra, 1951). Using physically plausible circumstances, an exact model of the universe is presented by obtaining the solutions of the Einstein’s field equations. Important geometrical and dynamical parameters of the model universes are premeditated and physical significance regarding their prospect in modern cosmology are discussed in details. Interestingly it is seen that both bulk viscosity and quadratic equation of state are acting crucial jobs throughout the evolution of the model which is expanding with acceleration so it represents dark energy model universe. Hence our model can be thought as a realistic universe. 相似文献
9.
Some Bianchi Type IX string cosmological models with bulk viscous fluid for massive string is investigated. To get a determinate
solution, a supplementary condition a=b
n, between metric potentials, is used wherea and b are function of time alone. A particular solution for n=0 is also discussed. The behaviour of the model in presence and absence
of bulk viscosity, is discussed. The physical and implications of the model is also discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
10.
In this paper we constructed five dimensional axially symmetric cosmological model generated by a cloud of strings with particles
attached to them in Lyra manifold. Out of the two different cases obtained one case leads to the five dimensional vacuum universe
in general theory of relativity while the other case yields a string cosmological model in Lyra manifold. In the cosmic string
model we observed that the sum of tension density and rest energy density of strings vanishes and this model is also inflationary. 相似文献
11.
Bianchi Type I string dust cosmological models in presence and absence of magnetic field following the techniques used by
Letelier and Stachel, are investigated. To get the deterministic solution, we have assumed that σ
11 is proportional to the expansion (θ) where σ
11 is the eigen value of shear tensor (σ
i
j
) and which leads to A=N(BC)−n
, n>0 where A,B,C are metric potentials and
, N and ℓ are constants. The behaviour of the models in presence and absence of magnetic field are discussed. The other physical and
geometrical aspects of the model are also discussed. 相似文献
12.
T. Vinutha V. U. M. Rao Bekele Getaneh Molla Mengesha 《Astrophysics and Space Science》2018,363(9):188
In this paper we have studied the anisotropic Kantowski-Sachs, locally rotationally symmetric (LRS) Bianchi type-I and LRS Bianchi type-III geometries filled with dark energy and one dimensional cosmic string in the Saez-Ballester theory of gravitation. To get physically valid solution we take hybrid expansion law of the average scale factor which is a product of power and exponential type of functions that results in time dependent deceleration parameter (\(q\)). The equation of state parameter of dark energy (\(\omega _{\mathit{de}}\)) has been discussed and we have observed that for the three models it crosses the phantom divide line (\(\omega _{\mathit{de}} = -1\)) and shows quintom like behavior. The density of dark energy (\(\rho _{\mathit{de}}\)) is an increasing function of redshift and remains positive throughout the evolution of the universe for the three models. Moreover in Kantowski-Sachs and LRS Bianchi type-I geometries the dark energy density dominates the string tension density (\(\lambda \)) and proper density (\(\rho \)) throughout the evolution of the universe. The physical and geometrical aspects of the statefinder parameters (\(r,s\)), squared speed of sound (\(v_{s}^{2} \)) and \(\omega _{\mathit{de}}\)–\(\omega ^{\prime }_{\mathit{de}}\) plane are also discussed. 相似文献
13.
We show the evolution of the Szekeres's cosmological models of class II with dissipative fluids and we study under which conditions these tend to the homogeneous and isotropic models. 相似文献
14.
This paper deals with the general class of Bianchi cosmological models with bulk viscosity and particle creation described by full causal thermodynamics in Brans-Dicke theory. We discuss three types of average scale-factor solutions for the general class of Bianchi cosmological models by using a special law for the deceler- ation parameter which is linear in time with a negative slope. The exact solutions to the corresponding field equations are obtained in quadrature form and solutions to the Einstein field equations are obtained for three different physically viable cosmologies. All the physical parameters are calculated and discussed in each model. 相似文献
15.
This paper is devoted to the study of role of particle creation and bulk viscosity on evolution of homogeneous and anisotropic
model of the universe represented by Bianchi type I space time metric. Particle creation and bulk viscosity have been considered
as separated irreversible processes. In order to discuss physical and geometrical behaviour of the model, a new set of exact
solutions of Einstein’s field equation have been obtained in non-causal, truncated and full causal theories. Dynamical behaviours
of models have also been discussed. 相似文献
16.
A. A. Saaryan 《Astrophysics》1995,38(2):164-175
We consider multi-dimensional cosmological models in the low-energy field theory of strings with a boson gravitational sector containing a metric, dilaton field, and antisymmetric Kalb-Ramon field. We study the conformal properties of the action and show that in the general conformal representation the theory is equivalent to a generalized scalar-tensor theory with a Lagrangian of nongravitating matter dependent on the dilaton. We find exact solutions of the flat homogeneous anisotropic model with structure R×M1×...×Mn and with equation of state pi=ai in the space Mi. We discuss the picture of cosmological evolution in different conformal representations.Translated fromAstrofizika, Vol. 38, No. 2, 1995. 相似文献
17.
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
18.
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
19.
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
20.
We obtain some cosmological models that are exact solutions of Einstein's field equations. The metric utilized is Marder's metric which is Bianchi Type I and the curvature source is a cloud of strings which are one dimensional objects. Bianchi type cosmological models play an important role in the study of the universe on a scale which anisotropy is not ignored. In this paper we have investigated the effect of cosmic strings on the cosmic microwave background anisotropy. Various physical and geometrical properties of the model are also discussed. The solutions have reported that the cosmic microwave background anisotropy may due to the cosmic strings. 相似文献