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1.
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
2.
Static and non-static plane symmetric string cosmological models are obtained in Lyra [Mathematische Zeitsehrift 54, 52, 1951] manifold. Some properties of the models are also discussed. 相似文献
3.
By adopting the co-moving coordinate system, an exact axially symmetric cosmological model with string dust cloud source is obtained in the framework of Brans-Dicke [Phys. Rev. 124, 925, (1961) Scalar – tensor theory of gravitation. Some physical and kinematical properties of the model are also discussed. 相似文献
4.
Axially symmetric string cosmological models are obtained in a scalar- tensor theory of gravitation proposed by Brans and
Dicke (Phys. Rev. 124:925, 1961). Some physical and geometrical properties of the models are also discussed. The models are anisotropic and free from singularities. 相似文献
5.
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
6.
Axially symmetric cosmological models are obtained in a scalar tensor theory proposed by Sen (Z. Phys. 149:311, 1957) based on Lyra manifold with time dependent β in the presence of string source, perfect fluid distribution, dust distribution and thick domain walls. Some physical and geometrical properties of these models are discussed. 相似文献
7.
Plane Symmetric string cosmological models are presented in Barber’s second self creation theory of gravitation and obtained
Einstein’s plane symmetric string cosmological models as a special case. Some physical and geometrical properties of the models
are also discussed. 相似文献
8.
By adopting the comoving coordinate system, the axially symmetric models with string dust cloud source are obtained. Some of these models are singular free even at an initial epoch, where the geometric as well as thep-strings become singular. 相似文献
9.
D. R. K. Reddy CH. C. S. V. V. R. Murthy R. Venkateswarlu 《Astrophysics and Space Science》2006,301(1-4):79-82
Field equations in the presence of a perfect fluid distribution are obtained in a scalar-tensor theory of gravitation proposed
by Saez and Ballester (Phys. Lett. 113, 1985, 467) with the aid of Einstein–Rosen cylindrically symmetric metric. A static vacuum model and a non-static stiff fluid
model are presented. The physical and geometrical properties of the stiff fluid model are studied. 相似文献
10.
S. K. Tripathy S. K. Nayak S. K. Sahu T. R. Routray 《Astrophysics and Space Science》2009,323(1):91-96
Bianchi type-I string cosmological models are studied in Saez-Ballester theory of gravitation when the source for the energy
momentum tensor is a viscous string cloud coupled to gravitational field. The bulk viscosity is assumed to vary with time
and is related to the scalar expansion. The relationship between the proper energy density ρ and string tension density λ are investigated from two different cosmological models. 相似文献
11.
We study the physical behavior of a five dimensional non-static spherically symmetric cosmological models in the presence of massive strings in the framework of \(f(R,T)\) gravity proposed by Harko et al. (Phys. Rev. D 84:024020, 2011). Here \(R\) is the Ricci scalar and \(T\) is the trace of the stress energy tensor and the fifth dimension is not observed because it is compact. We solve the field equations (i) using a relation between the scale factors given by Samantha and Dhal (Int. J. Theor. Phys. 52:1334, 2013) and (ii) equations of state for string models. The models obtained correspond to \(p\)-string, geometric string and massive string models in this modified theory in five dimensions. Cosmological parameters of the models are determined and their dynamical properties are discussed. 相似文献
12.
Bianchi type-I string cosmological models are obtained in bimetric theory of gravitation proposed by Rosen (Gen. Relativ. Gravit. 4:435, 1973). Established the existence of string cosmological models, unlike the earlier authors, in this theory and studied some physical and geometrical properties. 相似文献
13.
In this paper, it is shown that five dimensional LRS Bianchi type-I string cosmological models do not survive for Geometric
and Takabayasi string whereas Barotropic string i.e. ρ=ρ(λ) survives and degenerates string with ρ+λ=0 in scalar tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1986). Further we studied some physical and geometrical properties of the model. 相似文献
14.
Bianchi type-IX space-time is considered in the presence of cosmic string source in the frame work of a scalar- tensor theory
of gravitation proposed by Saez and Ballester (Phys. Lett. A 113:467, 1985). Exact cosmological models representing geometric (Nambu) string, p string and baratropic string are discussed in this theory.
Some physical and kinematical properties of the models are also studied. 相似文献
15.
Xing-Xiang Wang 《Astrophysics and Space Science》2004,293(4):433-440
Some locally rotationally symmetric (LRS) Bianchi type I cosmological models for a cloud string with bulk viscosity and magnetic
field are presented. Where an equation of state ρ = kλ and a relation between metric potential R = AS
n are considered. The solution describes a shearing and nonrotating model with a big bang start. In the absence of magnetic
field it reduces to a string model with bulk viscosity, where the relation between the coefficient of bulk viscosity and energy
density is ζ ∝ ρ1/2. After choosing k =
, it further reduces to a string model without viscosity and magnetic field.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
The present study deals with locally rotationally symmetric (LRS) Bianchi type II cosmological model representing massive
string. The energy-momentum tensor for such string as formulated by Letelier (Phys. Rev. D 28:2414, 1983) is used to construct massive string cosmological model for which we assume that the expansion (θ) in the model is proportional to the shear (σ). This condition leads to A=B
m
, where A and B are the metric coefficients and m is proportionality constant. For suitable choice of constant m, it is observed
that in early stage of the evolution of the universe string dominates over the particle whereas the universe is dominated
by massive string at the late time. Our model is in accelerating phase which is consistent to the recent observations of type
Is supernovae. Some physical and geometric behavior of the model is also discussed. 相似文献
17.
A. A. Saaryan 《Astrophysics》1995,38(3):248-260
We carry out an analysis of the exact solution obtained in the first part of this work for a homogeneous and anisotropic flat cosmological model in the general conformal representation of multidimensional low-energy string theory. We show that the singular solutions with power law of variation of the scale factors of maximally symmetric subspaces and scalar field are asymptotes of the general solution in early and late stages of evolution. We study the conditions under which models of exponential, extended, and violent inflation are realized. As an illustration of the general regularities we consider the specific example of an antisymmetric Kalb-Ramond field as a gravitational source. We demonstrate the possibility of dynamic compactification of the extra dimensions.Translated fromAstrofizika, Vol. 38, No. 3, 1995. 相似文献
18.
Assuming the time-dependent equation of state p=λ(t)ρ, five dimensional cosmological models with viscous fluid for an open universe (k=−1) and flat universe (k=0) are presented. Exact solutions in the context of the rest mass varying theory of gravity proposed by Wesson (Astron. Astrophys.
119, 145, 1983) are obtained. It is found that the phenomenon of isotropisation takes place in this theory, i.e. the mass scale factor A(t) which characterizes the rest mass of a typical particle is evolving with cosmic time just as the spatial scale factor R(t). It is further found that rest mass is approximately constant in the present universe. 相似文献
19.
In this paper, we have investigated plane symmetric inhomogeneous cosmological models in the presence of massless scalar field
in modified theory of general relativity when source of the gravitational field is a perfect fluid. The physical and geometrical
aspects of the models together with singularity involved in the models are also discussed.
PACS Nos.: 04.50. + h•4.20.Cv• 4.20.Dw 相似文献
20.
The correspondence principle offered a unique opportunity to test cylindrically symmetric model for Universe at correspondence point “the centre of mass energies around (M s/(g s)2)”. First by using this symmetry, the Universe state for highly excited string “string ball” is studied and the entropy of these states is calculated. Then, to consider the string ball states, a copy of the original Hilbert space is constructed with a set of creation/annihilation operators that have the same commutation properties as the original ones. The total Hilbert space is the tensor product of the two spaces H physical ?H unphysical , where in this case H physical denotes the physical quantum state space of the string ball. It is shown that string ball states can be represented by a maximally entangled two-mode squeezed state of the physical and unphysical spaces of string. Also, the entropy for these string states is calculated. It is found that Universe entropy matches the string entropy at transition point. This means that our result is consistent with correspondence principle and thus cylindrically symmetric model works. Finally the signature of bosonic string ball is studied. When string balls are produced, they evaporate to Massive particles like Higgs boson. Then Higgs bosons decay to quarks and gluons. Thus an enhancement of these partons can be a signature of bosonic string ball inside the cylindrically symmetric Universe. 相似文献