Homogeneous anisotropic cosmological models with viscous fluid and magnetic field

The paper presents some exact solutions of Bianchi types I and III and Kantowski-Sachs cosmological models consisting of a dissipative fluid along with an axial magnetic field. A barytropic equation of state (p=), together with a pair of linear relations between the matter density (), the shear scalar (), and the expansion scalar () have been assumed for simplicity. The solutions are basically of two different types, one for the Bianchi I and the other for III and Kantowski-Sachs type. The presence of the magnetic field, however, does not change the fundamental nature of the initial singularity.     

Boltzmann and Vlasov kinetic equations in anisotropic cosmological models

The structure of the Boltzmann and Vlasov Kinetic equations is considered for spatially uniform cosmological models taking into account the Einstein equations. A successive approximation technique is proposed for solving Boltzmann's equation at the intensely anisotropic vacuum stage of expansion for the type I Bianci cosmological model. It is shown that during the hadron stage the collisional gas can be found in a highly nonequilibrium state.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 28–33, 1986.     

Solving Bertolami's equations for Brans-Dicke cosmological models

Solutions are developed for Berman and Som's formulation of Bertolami's equations for a Brans-Dicke cosmology with time-dependent cosmological term. Physical constraints are applied to these solutions to deduce conditions necessary for constructing plausible cosmological models in this theory.     

Cylindrically symmetric inhomogeneous cosmological models with viscous fluid and varying Λ

Cylindrically symmetric non-static cosmological models representing a bulk viscous fluid distribution have been obtained which are inhomogeneous and anisotropic. Without assuming anyadhoc law, we obtain a cosmological constant as a decreasing function of time. Various physical and geometrical features of the models are also discussed.     

The superfluid vacuum state,time-varying cosmological constant,and nonsingular cosmological models

Some cosmological consequences of the superfluid vacuum state developed previously by the authors are discussed, particularly with regard to the initial stages of the universe. The transition temperature of the hadronic superfluid (superfluid during the hadron era) is estimated to be 10 ¹³ K, which is the same as the Hagedorn temperature, giving a physical basis of the thermodynamic bootstrap model.     

Particle production in a viscous cosmological fluid

The dynamical and thermodynamical effects of a bulk viscous pressure and particle production on the early universe are analyzed in the framework of open thermodynamical systems. Analytical solutions are obtained for particle number density, temperature and entropy for most of the models.     

Charge in cosmological models

The balanced field equations due to Penney are used to find solutions for cosmological models in the presence of charge. Herein, it is found that the introduction of charge adds additional terms to the Einstein conservation equation and distribution expressions. The curvature parameter is affected and it is concluded that whereas matter affects it positively, the charge does so negatively. There then arises also the possibility of an evolution of local systems against the background of a global expansion.     

Slow rotation of compressible viscous fluid in cosmological universe

New analytic solutions for rotational perturbations of the Robertson-Walker metric are found in order to incorporate the possibility of a rotating viscous universe. The field equations impose restrictions on the matter rotationω(r, t), and some of the solutions for Ω(r, t) which is related to the local dragging of inertial frames are studied. In all the cases the rotational velocity is found to decay with increase of time. Geodesics of the metric are studied to reveal the intrinsic nature of rotation and to elucidate the role of Ω.     

Oscillatory behavior in cosmological models

Oscillatory behavior in cosmological models is investigated, motivated, in part, by the apparent periodic distribution of galaxies in deep narrow-cone red-shift surveys. In particular, oscillatory behavior in two cosmological models is studied; a qualitative analysis is performed and approximate solutions are found for a soft inflationary model and for a Friedmann-Robertson-Walker model containing a perfect fluid and a scalar field source. These two models are conformally equivalent to particular models arising from a large class of scalar-tensor theories. It is then argued that such oscillatory behavior is a generic property of scalartensor theories of gravity.     

量子纠缠与宇宙学弗里德曼方程

量子纠缠作为量子信息理论中最核心的部分,代表量子态一种内在的特性,是微观物质的一种根本的性质,它是以非定域的形式存在于多子量子系统中的一种神奇的物理现象.熵也是量子信息理论的重要概念之一,纠缠熵作为量子信息的一个测度已经成为一种重要的理论工具,为物理学中的各类课题提供了新的研究方法.本文主要考虑量子纠缠的宇宙学应用,试图更好地从纠缠的角度来理解宇宙动力学.本文研究了量子信息理论的概念和宇宙学之间的深层联系,利用费米正则坐标和共形费米坐标构建了弗里德曼- 勒梅特-罗伯逊-沃尔克宇宙学弗里德曼方程和纠缠之间的联系.假设小测地球（a geodesic ball）的纠缠熵在给定体积下是最大的,可以从量子纠缠第一定律推导出弗里德曼方程.研究表明引力与量子纠缠之间存在着某种深刻的联系,这种联系对引力场方程的解是成立的.     

Quantum statistics in cosmological models

The properties and evolution of a Friedmann universe filled with a quantum gas of massless particles and massive dust are investigated on the basis of quantum statistics. Values are given for the critical temperature and the Fermi temperature, and the possibility of degeneracy of the neutrino gas is shown. The expressions obtained for the Fermi energy are applied for estimates of the neutrino density in the Universe.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 61–65, May, 1981.     

Bochner techniques and cosmological models

We demonstrate the possibility of applying the Bochner techniques [R. Zh. Matematika, 2A, 746 (1985)] to dynamics of an ideal fluid in a curved space-time. One example of the result of such application is that every irrotational motion of cosmological fluid with zero expansion in a closed oriented space-time obeying the energy condition is shearless.Vladimir State Pedagogical Institute. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 6, pp. 82–86, June, 1993.     

Bianchi Type-IX viscous fluid cosmological model in general relativity

Bianchi Type-IX viscous fluid cosmological model is investigated. To get a deterministic model, we have assumed the conditiona = b ^m(m is a constant) between metric potentials andη ∞θ whereη is the coefficient of shear viscosity andθ the scalar of expansion in the model. The coefficient of bulk viscosity (ς) is taken as constant. The physical and geometrical aspects of the model are also discussed.     

Generalized expanding and shearing magnetized viscous fluid cosmological model

We investigate the behavior of a magnetic field in a viscous fluid cosmological model where the expansion in the model is proportional to ₁ ¹ , the component of shear tensor _i ^j , which leads to A=(Bc)ⁿ. We also assume that the shear viscosity is proportional to the rate of expansion in the model. The behavior of the model in the absence of a magnetic field and viscosity is discussed as are some other physical and geometrical aspects.     

Soluble Boltzmann equations for internal state and Maxwell models

We consider a class of scalar nonlinear Boltzmann equations describing the evolution of a microcanonical ensemble in which sub-systems exchange internal energy ‘randomly’ in binary interactions.In the continuous variable version these models can equally be interpreted as Boltzmann equations for Maxwell type molecules in arbitrary dimensionality.We construct general solutions in the form of a Fourier series; the expansion coefficients (Sonine or Meixner moments) satisfy the same recursive system of coupled equations as the ordinary moments, and can be solved sequentially.     

Construction of spinor-field equations in cosmological space

The embedding method is employed to construct the spinor-field equation in curved space. The equivalence conditions are given for spinor-field equations in the original curved 4-space and in the flat 6-space of embedding.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 15, No. 10, pp. 20–25, October, 1972.The authors would like to express their gratitude to Professor D. Ivanenko for discussing this problem with them.     

An assessment of additional terms in the macroscopic Einstein equations in cosmology. Nonsingular cosmological models

This work deals with the estimation of additional terms in a macroscopic set of the Einstein-Maxwell equations as applied to cosmology and the problem of construction of nonsingular cosmological models.__________Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 21–26, December, 2004.     

Bianchi types I and V bulk viscous fluid cosmological models in f(R,T) gravity theory

In this paper we present non-singular Bianchi types I and V cosmological models, in the presence of bulk viscous fluid and within the framework of f(R,T) gravity theory. Exact solutions to the field equations are obtained by choosing a particular form of the function f(R,T) and a special value for the average scale factor of the model, which corresponds to a time- dependent deceleration parameter. The cosmological models initially accelerate for a certain period of time and thereafter decelerate. The physical and kinematical properties of the models of the universe are discussed.