共查询到20条相似文献，搜索用时 15 毫秒
1.
The evolution of a homogeneous, isotropic cosmological model driven by a nonminimally coupled scalar field is studied. The
potential for the quintessential inflation model proposed by Peebles and Vilenkin is selected as a scalar potential. Possible
scenarios for the cosmological dynamics are described in the conformal Einstein and Jordan representations. It is shown that,
unlike in models with a minimal scalar field, here a class of solutions exists for which the scalar field is fixed at finite
values during cosmological expansion.
__________
Translated from Astrofizika, Vol. 49, No. 3, pp. 487–498 (August 2006). 相似文献
2.
Harald H. Soleng 《Astrophysics and Space Science》1987,137(2):373-384
Two exact solutions of Einstein's field equations of vacuum are presented and investigated. We will regard the term vacuum fluid as the limiting case of scalar field with an almost constant potential. Considering the four velocity of this fluid we find, that in both solutions there is an anisotropic expansion of the cosmic fluid, but the fluid has vanishing vorticity.We investigate whether shear could prevent the transition into an inflationary era in these models, and the effect of shear on a scalar field is also considered. It is found that shear will speed up the rollover of the scalar field in some Bianchi type-VIII models.Possible initial conditions are discussed in light of the group structures of the models. 相似文献
3.
The scalar field theory on the background of cosmological models with n(n ≥ 1) spaces of constant curvature is considered. We take the integrable case of Ricci flat internal spaces. The coupling between the scalar and the gravitational fields includes the minimal coupling as well as the conformal case. In the ground state of the scalar field we find the conditions for vacuum instability realized for most of the possible solutions to Einstein's equations if the coupling parameter takes appropriate values. For the excited states of the scalar field we show the induction of massive modes and discuss their properties. 相似文献
4.
It is shown that in the most general version of the bimetric scalar-tensor theory of gravitation, a spherically symmetric
vacuum gravitational field is static if the gravitational scalar does not depend on time. This result is generalized to certain
cases in which a source is present, including an electromagnetic field. Both branches of solutions with a variable and a constant
scalar field are considered.
Translated from Astrofizika, Vol. 40, No. 2, pp. 281–290, April–June, 1997. 相似文献
5.
D. R. K. Reddy 《Astrophysics and Space Science》1988,140(1):85-88
A result having formal similarity to Birkhoff's theorem in general relativity is proved, both in vacuum as well as in the presence of electromagnetic fields, in a conformally-invariant scalar field theory with trace-free energy-momentum tensor for the special case when the scalar field is independent of time. 相似文献
6.
K.-H. Rdler 《Astronomische Nachrichten》1972,294(5):213-224
This paper deals with the mathematical treatment of special models of hydromagnetic dynamos. For the models considered here the conducting medium occupies a spherical region surrounded by vacuum. Both laminar and turbulent dynamos are included. The partial vector differential equations governing the models are transformed into an infinite set of differential equations for scalar functions by applying a method previously used by BULLARD and GELLMAN and on the basis of a representation of vector fields as a sum of a poloidal and a toroidal part. The scalar functions depend only on a radial coordinate and possibly on the time. In both the stationary and the periodic case, an infinite set of ordinary differential equations results which may be treated numerically. A series of relations for computing various dynamo models is prepared. 相似文献
7.
8.
Rotational perturbations of charged cosmological viscous-fluid universes coupled with a scalar field
Manihar Singh Koijam 《Astrophysics and Space Science》1989,162(1):129-150
The dynamics of a slowly rotating charged viscous-fluid Universe coupled with a zero-mass scalar field is investigated; and the rotational perturbations of such models are studied in order to substantiate the possibility that the Universe is endowed with slow rotation, in the course of presentation of several new analytic solutions. The effects of charged field and scalar field on the rotational motion are discussed. Except for perfect dragging, the scalar field as well as the charged field is found to have a damping effect on the rotation of matter. Rotating models which are expanding as well are obtained, in which cases the rotational velocities are found to decay with the time, and these models may be taken as good examples of real astrophysical situations. The periods of physical validity of different models are also obtained. 相似文献
9.
This is the second paper of the series where we have considered Brans-Dicke (B-D) theory as well as general scalar tensor
theory of gravitation in higher dimensional space-time model in the false vacuum state. We have examined whether inflationary
solutions are possible both for constant or variable coupling parameter ω. Also the nature of the scalar field and the coupling
parameter are discussed in the asymptotic limit.
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 some cosmological models in five dimensional LRS Bianchi type-V space time based on general theory of relativity. Further, it is shown that source density of the meson field does not survive either in massive scalar field or in mass less scalar field. Some physical and geometrical properties of the models are discussed. 相似文献
11.
Recently Lau & Prokhovnik (1986) have formulated a new scalar-tensor theory of gravitation which reconciles Dirac’s large
numbers hypothesis with Einstein’s theory of general relativity. The present work points out an error in the time-dependent
cosmological term and the scalar potential given by Lau and Prokhovnik. The correct forms for these quantities are derived.
Further, a vacuum Robertson-Walker solution to the generalized field equations is obtained, under an anasatz that we propose,
which illustrates that the theory is, in some sense, incomplete. 相似文献
12.
Garth A. Barber 《Astrophysics and Space Science》2002,282(4):683-730
A theory is described which produces continuous creation by adapting that of Brans-Dicke. The universe is seen to be created
out of the zero point energy field by self-contained gravitational, scalar, and matter fields. The theory is conformally equivalent
to General Relativity in vacuo.Both the Jordan and the Einstein frames are physical and they conserve energy and four-momentum respectively. The conformal
equivalence has the consequence that predictions of the theory in solar system experiments are identical with General Relativity,
but definitive experiments exist which distinguish between the two theories. The cosmological solution yields a linear expansion
with a dynamical density parameter Omega of
anda cold matter density parameter of
, but the universe is closed. The theory is free of the horizon, smoothness and density problems of GR and therefore does
not need Inflation. It does however require an exotic equation of state with negative pressure and it is suggested that this
is provided by a false vacuum or zero point energy determined, and there forelimited by, its field equations thereby overcoming
the ‘lambda problem’.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
13.
Morteza Yavari 《Astrophysics and Space Science》2013,348(1):293-302
The f(R) theories of gravity have been interested in recent years. A considerable amount of work has been devoted to the study of modified field equations with the assumption of constant Ricci scalar which may be zero or nonzero. In this paper, the exact vacuum solutions of plane symmetric spacetime are analyzed in f(R) theory of gravity. The modified field equations are studied not only for R=constant but also for general case R≠constant. In particular, we show that the Novotný-Horský and anti-de Sitter spacetimes are the exact solutions of the field equations with the non-zero constant Ricci scalar. Finally, the family of solutions with R≠constant is obtained explicitly which includes the Novotný-Horský, Kottler-Whittaker, Taub and conformally flat spacetimes. 相似文献
14.
A. L. Mkhitaryan 《Astrophysics》2009,52(4):598-608
Quantum effects for a scalar field are studied in Friedmann-Robertson-Walker cosmological models witha power-law scaling factor
and a Rp × (S1)q spatial topology. Recurrence formulas are obtained for thepositive-frequency Wightman function and the vacuum average squared
field. The asymptotic behavior of the vacuum average is studied in the early and late stages of cosmological evolution. 相似文献
15.
《天文和天体物理学研究(英文版)》2016,(4)
On studying some new models of Robertson-Walker universes with a Brans-Dicke scalar field, it is found that most of these universes contain a dark energy like fluid which confirms the present scenario of the expansion of the universe. In one of the cases, the exact solution of the field equations gives a universe with a false vacuum, while in another it reduces to that of dust distribution in the Brans-Dicke cosmology when the cosmological constant is not in the picture. In one particular model it is found that the universe may undergo a Big Rip in the future, and thus it will be very interesting to investigate such models further. 相似文献
16.
Vladimir V. Sokolov 《Astrophysics and Space Science》1992,191(2):231-258
In the bounds of the consistent dynamic interpretation of gravitation (gravidynamics) a gravitational field has been divided into two components: scalar and tensor, each one interacting with its source by the same coupling constant. Consequently, a spherically-symmetrical gravitational field in vacuum generated by a massive object influences test bodies as an algebraic sum of attraction and repulsion. Field energy in vacuum around the source is also a sum of energies of two components — purely tensor and scalar ones of gravitation. At distances from a gravitating object much greater than its gravitational radius, energies of each separate field component are equal to each other at the same point of space.In the bounds of gravidynamics based on the so-called Einstein's linearized equation and proceeding from general principles of theory of classical fields a statement (a theorem) has been formulated on the static gravitational field of a collapsar: a spherically-symmetric object generating a static field in vacuum may always only occupy a finite, nonzero volume. 相似文献
17.
Eric G. Blackman 《Monthly notices of the Royal Astronomical Society》2001,323(2):497-505
In addition to the scalar Shakura–Sunyaev α ss turbulent viscosity transport term used in simple analytic accretion disc modelling, a pseudo-scalar transport term also arises. The essence of this term can be captured even in simple models for which vertical averaging is interpreted as integration over a half-thickness and each hemisphere is separately studied. The additional term highlights a complementarity between mean field magnetic dynamo theory and accretion disc theory treated as a mean field theory. Such pseudo-scalar terms have been studied, and can lead to large-scale magnetic field and vorticity growth. Here it is shown that vorticity can grow even in the simplest azimuthal and half-height integrated disc model, for which mean quantities depend only on radius. The simplest vorticity growth solutions seem to have scales and vortex survival times consistent with those required for facilitating planet formation. In addition, it is shown that, when the magnetic back-reaction is included to lowest order, the pseudo-scalar driving the magnetic field growth and that driving the vorticity growth will behave differently with respect to shearing and non-shearing flows: the former pseudo‐scalar can more easily reverse sign in the two cases. 相似文献
18.
It is show that axisymmetric stationary vacuum solutions of the general scalar tensor theory of gravitation proposed by Nordvedt and later discussed by Barker and others can be obtained from the solutions of the axisymmetric stationary Einstein vacuum fields and also from the axisymmetric static vacuum fields of the general scalar tensor theory. The scalar tensor analogue of the Kerr solution has been obtained. 相似文献
19.
A. A. Saharian 《Astrophysics》2000,43(1):92-101
A new mechanism is proposed for stabilization of the scalar dilaton field within the framework of lowenergy string gravitation
with loop corrections to the dilaton coupling functions. It is based on the assumption that the loop corrections generate
a kinetic dilaton function, which is singular for some finite value of the dilaton field. For a nongravitational source of
the barotropic type, the system of equations describing the evolution of homogeneous and isotropic cosmological models is
represented in the form of a thirdorder, autonomous, dynamical system. The behavior of the general solution in the vicinity
of singularities of the dilaton coupling function is investigated by methods of the qualitative theory of dynamical systems.
It is shown that there is a class of solutions, different from solutions of the general theory of relativity, with a constant
dilaton. The conditions under which these solutions are an attractor for a general solution with a variable dilaton are determined.
Translated from Astrofizika, Vol. 43, No. 1, pp. 123-136, January–March, 2000. 相似文献
20.
A variant of the Jordan-Brans-Dicke (JBD) theory is examined which contains a cosmological scalar that is written so that on going to the Einstein representation it becomes the ordinary cosmological constant of general relativity theory. This paper is divided into two parts. In Part I we examine the cosmological solutions for the Einstein representation of the JBD theory, i.e., in the presence of a minimally coupled scalar field. In Part II we shall study the cosmological solutions in the proper representation of the JBD theory with a self consistent scalar field. The analysis of these solutions is of interest in connection with modern concepts of the evolution of the universe, in particular, with the observed acceleration of cosmological expansion and estimates of the density of dark matter and dark energy.__________Translated from Astrofizika, Vol. 48, No. 3, pp. 455–462 (August 2005). 相似文献