Bianchi Type I string dust cosmological model with magnetic field in general relativity

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.     

Exact Nonbarotropic Bianchi Type I Universe

Bianchi type I cosmological models are studied that contain a nonbarotropic relativistic Boltzmann gas. The effect of a cosmological constant is considered too. In the limit of small temperatures the general solution of the Einstein gravitational field equations can be expressed in an exact closed parametrical form. At final stages, depending on the presence or absence of the cosmological constant, cosmologies are driven to an isotropic inflationary de Sitter Universe or to an isotropic Friedmann era. This revised version was published online in July 2006 with corrections to the Cover Date.     

Massive scalar field interacting with viscous fluid distribution in cosmological models

The study of Einstein's field equations describing Robertson-Walker cosmological models with massive scalar field and viscous fluid representing the matter has been made. The problem has been investigated with and without the source density in the wave equation. Corresponding exact solutions of the field equations have been obtained under different physical equations of state: namely, (i) dust distribution, (ii) Zeldovich fluid distribution, (iii) disordered distribution of radiation subject to physically realistic conditions. The physical interpretations of the physically realistic solutions has been investigated. It has been found that physically realistic solutions has been obtained for closed cosmological models only.     

Bianchi type I vacuum,field in Brans-Dicke theory

An exact solution of the vacuum Brans-Dicke field equations is obtained for the metric tensor of a spatially-homogeneous and anisotropic Bianchi type I configuration. The solution has no analogy in Einstein's theory for the layer values of the BD parameter. Some properties of the solution are discussed.     

Mesonic stiff fluid distribution in five dimensional Bianchi type space time

In this paper, we have constructed mesonic stiff fluid cosmological models in five dimensional LRS Bianchi type-I and Bianchi type-VI₀ space times in general theory of relativity. Some physical and geometrical properties of the models are discussed.     

Bianchi I型宇宙中矢量暴涨理论相关问题的研究

通过矢量暴涨理论,研究了与之相关的问题,特别是粒子生成对慢滚过程、相图以及各向异性的影响.计算结果表明,粒子生成对标量场的影响使得相图上出现一个峰,峰的方向不受初始条件和质量改变的影响.而对于矢量场,情况则不同,粒子生成对应的峰其方向会改变,这与质量的变化有关.相应地,体系的各向异性也会随之增强或减弱.各向异性的程度不仅决定于慢滚过程,还决定于慢滚后的粒子生成过程.粒子生成可以成为宇宙各向同性化的原因.     

Some string cosmological models in Bianchi Type I space-time

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.     

Massive cosmic strings in Bianchi type II

We study a massive cosmic strings with BII symmetries cosmological models in two contexts. The first of them is the standard one with a barotropic equation of state. In the second one we explore the possibility of taking into account variable “constants” (G and Λ). Both models are studied under the self-similar hypothesis. We put special emphasis in calculating the numerical values for the equations of state. We find that for ω∈(0,1], G, is a growing time function while Λ, behaves as positive decreasing time function. If ω=0, both “constants”, G and Λ, behave as true constants.     

Strange quark matter attached to string cloud in Bianchi type-III space time

We have obtained Bianchi type-III cosmological model with strange quark matter attached to the string cloud in general relativity. For solving the Einstein’s field equations the relation [C=A ⁿ ] between metric coefficients C and A is used. Also, some physical and kinematic properties of the model are discussed.The results are analogous to results obtained by Yilmaz (Gen. Rel. Grav. 38:1397–1406, 2006).     

Bianchi type-I universe in the presence of zero-mass scalar fields

An exact Bianchi type-I cosmological model in the presence of zero-mass scalar fields is obtained when the source of the gravitational field is a perfect fluid with pressure equal to energy density. Some properties of the model are discussed.     

Bianchi Type I Magnetized String Cosmological Model in General Relativity

Bianchi Type I magnetized string cosmological model following the techniques used by Letelier and Stachel, is investigated. To get a determinate model, we assume a condition ∊ = λ (geometric string) where ∊ is the rest energy density, λ the string tension density and expansion (θ) is proportional to eigen value σ₁ ¹ of shear tensor (σ _j ⁱ ), which leads to A = ℓ (BC) ⁿ where A, B, C are metric potentials and ℓ and n are constants. The behaviour of the model in presence and absence of magnetic field is discussed. The physical and geometrical aspects of the model are also discussed.     

Viscous Fluid Cosmological Models in a Bianchi Type I Universe

Exact solutions of the gravitational field equations for a Bianchi type I anisotropic space-time, filled with a viscous cosmological fluid obeying an equation of state of the form p = , 0 1, are obtained. We investigate both the viscous Zeldovich ( = 1) and < 1 fluid cases, with constant and time varying (proportional to the mean Hubble factor) shear and bulk viscosity coefficients. It is shown that independently of the matter content, the equation of state and the time dependence of the shear and bulk viscosity coefficients, a viscous Bianchi type I universe experiences a transition to an inflationary era. Due to dissipative processes, the mean anisotropy and the shear of the Bianchi type I universe tend very rapidly to zero.     

Bianchi Type I Anisotropic Magnetized Cosmological Model in General Relativity

Bianchi Type I magnetized Cosmological model for perfect fluid distribution is investigated. The magnetic field is due to an electric current produced along x-axis. The distribution consists of an electrically neutral perfect fluid with an infinite electrical conductivity. To get a determinate solution, a supplementary conditionA = BC between metric potentials is used. The behaviour of the model in presence and absence of magnetic field is also discussed. This revised version was published online in July 2006 with corrections to the Cover Date.     

Massive scalar field quasinormal frequencies in black hole with a deficit solid angle

Massive scalar field quasinormal modes of black hole with a deficit solid angle are studied by using the third-order WKB approximation. From the numerical results obtained, we find that scalar field with higher mass u will oscillate more quickly but decay more slowly, while with larger deficit solid angle ε will oscillate and decay more slowly. Moreover, the imaginary parts of quasinormal frequencies are almost linearly related to the real parts with u and ε.     

Bianchi type-II,VIII, and IX cosmologies with conformally-invariant scalar field and electromagnetic fields

In the expansive nondecelerative universe creation of matter happens as a result of a fundamental relationship and mutual compatibility of the field and matter.     

Bianchi type-VI0 universe in the presence of zero-mass scalar fields

An exact Bianchi type-VI₀ cosmological model in the presence of zero-mass scalar fields is obtained when the source of the gravitational field is a perfect fluid with pressure equal to energy density. Some physical properties of the model are discussed.