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1.
A global excitation variable is introduced, as a conformal factor of the metric that depends only on time, into the Einstein
theory of gravitation formulated in terms of conformally invariant variables. The dynamics of this global excitation is isolated
from the Einstein equations by direct averaging of their dynamical part over large spatial volumes. The conditions are found
under which this dynamics duplicates the dynamics of the Friedmann cosmological model.
Translated from Astrofizika, Vol. 42, No. 3, pp. 457–464, July–September, 1999. 相似文献
2.
Modern concepts of the universe support the assumed existence of a nongravitational source, known as dark energy, for which
ε + 3 P < 0 (where ε is the energy density and P is the pressure). This ensures accelerated expansion of the universe. This paper examines a tensor-scalar
variant of the theory of gravitation with a conformally coupled scalar field. Various cosmological models are examined and
the possible evolutionary development of the universe with accelerated expansion is discussed.
Translated from Astrofizika, Vol. 51, No. 4, pp. 653–661 (November 2008). 相似文献
3.
Recent cosmological observations of large-scale structures (red shift of type Ia supernovae) confirm that the universe is
currently expanding at an accelerating rate and its dominant component is dark energy. This has stimulated the development
of the theory of gravity and led to many alternative variants, including tensor-scalar ones. This paper deals with the role
of conformal transformations in the Jordan-Brans-Dicke theory. Variants of intrinsic, conformally coupled, and Einstein representations
are examined. In the Einstein representation an exact analytic solution for the standard cosmological model is obtained. It
is expressed in terms of the relative energy contributions of ordinary matter Ω
m
, the scalar field Ω
CK
, and a term ΩΛ related to the cosmological constant Λ . Information on the evolution of the universe for the case with a minimally coupled
scalar field is given in the form of graphs. 相似文献
4.
Recently, exact spatially-homogeneous solutions have been found for a conformally invariant massless scalar fieldS(t) coupled to a Robertson-Walker geometry. We investigate extending these solutions to inhomogeneous scalar fieldsS(t, x
l
). For an isotropic scalar fieldS(t, r) we find a solution satisfying three of the five field equations. If we use REDUCE, we show that the remaining equations forceS=S(t). 相似文献
5.
Shri Ram 《Astrophysics and Space Science》1984,104(1):151-155
An exact solution of Einstein's equations corresponding to the conformally invariant scalar field with tracefree energy-momentum tensor as source is obtained in Bianchi type VI0 class of metrics. The solution represents a spatially homogeneous but anisotropy universe which admits anisotropic expansions. Some properties of the cosmological model are discussed. 相似文献
6.
Metod Saniga 《Astrophysics and Space Science》1993,207(2):301-304
Several authors have studied solutions of Einstein's field equations for a conformally invariant scalar field with trace-free energy-momentum tensor for the Robertson-Walker models forK = 0, ± 1. The relationship of these solutions to a previously existing one by Som (1985) is discussed. TheK = 0 model derived by Innaiah and Reddy (1985) is shown to be a special case of the Bianchi type-I models due to Accioly, Vaidya and Som (1983a). 相似文献
7.
A problem of static plane symmetric metric in the perfect fluid, the mesonic massive scalar field and in their coupling is
studied in Rosen’s (1973) bimetric theory of relativity. It was found that the matter field like either perfect fluid or mesonic
massive scalar field or their coupling does not survive in bimetric theory of gravitation when the space–time is governed
by n-dimensional static plane symmetric metric. 相似文献
8.
Mark Israelit 《Astrophysics and Space Science》1996,240(2):331-344
Dark matter is obtained from a scalar field coupled conformally to gravitation, the scalar being a relict of Dirac's gauge function. This conformally coupled dark matter includes a gas of very light (m 2.25 × 10–34
eV) neutral bosons having spin 0, as well as a time-dependent global scalar field, both pervading all of the cosmic space. The time-development of this dark matter in the expanding F-R-W universe is investigated, and an acceptable cosmological behaviour is obtained. 相似文献
9.
The present paper addresses the existence of J
2 invariant relative orbits with arbitrary relative magnitude over the infinite time using the Routh reduction and Poincaré
techniques in the J
2 Hamiltonian problem. The current research also proposes a novel numerical searching approach for J
2 invariant relative orbits from the dynamical system point of view. A new type of Poincaré mapping is defined from different
central manifolds of the pseudo-circular orbits (parameterized by the Jacobi energy E, the polar component of momentum H
z
and the measure of distance Δr between the fixed point and its central manifolds) to the nodal periods T
d
and the drifts of longitude of the ascending node during one period (ΔΩ), which differs from Koon et al.’s (AIAA 2001) definition on central manifolds parameterized by the same fixed point. The Poincaré mapping is surjective because it compresses
the three-dimensional variables into two-dimensional images, and the mapping degenerates into a bijective mapping in consideration
of the fixed points. An iteration algorithm to the degenerated bijective mapping is proposed from the continuation procedure
to perform the ergodic representation of E- and H
z
-contour maps on the space of T
d
–ΔΩ. For the surjective mapping with Δr ≠ 0, different pseudo-circular or elliptical orbits may share the same images. Hence, the inverse surjective mapping may
achieve non-unique variables from a single image, which makes the generation of J
2 invariant relative orbits possible. The pseudo-circular or elliptical orbits generated from the surjective mapping will be
defined in different meridian planes. Hence, the critical contribution of the present paper is the assignment of J
2 invariant relative orbits to different invariant parameters E and H
z
depending on the E- and H
z
-contour map, which will hold J
2 invariant relative orbits for extended durations. To investigate the high-order nonlinearity neglected by previous studies,
a formation configuration with a large magnitude of 500 km is successfully generated from the theory developed in the present
work, which is beyond the scope of the linear conditions of J
2 invariant relative orbits. Therefore, the existence of J
2 invariant relative orbit with an arbitrary relative magnitude over the infinite time is achieved from the dynamical system
point of view. 相似文献
10.
A model of the early universe in the Einstein theory of gravitation, supplemented by a conformalty invariant version of the
Weinberg—Salam model, is considered. The conformai symmetry principle leads to the need to eliminate the Higgs potential from
the expression for gravitational action, using the Lagrangian density of the model of Weinberg—Salam electroweak interactions
as the material source, and to incorporate the conformally invariant Penrose—Chernikov—Tagirov term. In the limit of flat
space, we arrive at the a version of the Weinberg—Salam model without Higgs particle-like excitations. In the conformalty
invariant model under consideration, Higgs fields are absorbed by the spatial metric, so one can assume that the masses of
elementary particles originate at the time when the evolution of the universe begins.
Translated from Astrofizika, Vol. 41, No. 3, pp. 459–471, July–September, 1998. 相似文献
11.
We revisit a set of symplectic variables introduced by Andre Deprit (Celest Mech 30, 181–195, 1983), which allows for a complete symplectic reduction in rotation invariant Hamiltonian systems, generalizing to arbitrary dimension
Jacobi’s reduction of the nodes. In particular, we introduce an action-angle version of Deprit’s variables, connected to the
Delaunay variables, and give a new hierarchical proof of the symplectic character of Deprit’s variables. 相似文献
12.
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
13.
14.
Recently, Innaiah and Reddy (1985) obtained a flat Robertson-Walker-type solution for the Einstein field equations with the trace-free energy-momentum tensor of a conformally invariant scalar field as source. Here we show that the field equations force the scalar field to be independent of time. Furthermore, we obtain open and closed Robertson-Walker-type solutions and observe that, once again, the scalar field has to be independent of time. 相似文献
15.
In the method of variation of parameters we express the Cartesian coordinates or the Euler angles as functions of the time
and six constants. If, under disturbance, we endow the “constants” with time dependence, the perturbed orbital or angular
velocity will consist of a partial time derivative and a convective term that includes time derivatives of the “constants”.
The Lagrange constraint, often imposed for convenience, nullifies the convective term and thereby guarantees that the functional
dependence of the velocity on the time and “constants” stays unaltered under disturbance. “Constants” satisfying this constraint
are called osculating elements. Otherwise, they are simply termed orbital or rotational elements. When the equations for the
elements are required to be canonical, it is normally the Delaunay variables that are chosen to be the orbital elements, and
it is the Andoyer variables that are typically chosen to play the role of rotational elements. (Since some of the Andoyer
elements are time-dependent even in the unperturbed setting, the role of “constants” is actually played by their initial values.)
The Delaunay and Andoyer sets of variables share a subtle peculiarity: under certain circumstances the standard equations
render the elements nonosculating. In the theory of orbits, the planetary equations yield nonosculating elements when perturbations
depend on velocities. To keep the elements osculating, the equations must be amended with extra terms that are not parts of the disturbing function [Efroimsky, M., Goldreich, P.: J. Math. Phys. 44, 5958–5977 (2003); Astron. Astrophys. 415, 1187–1199 (2004); Efroimsky, M.: Celest. Mech. Dyn. Astron. 91, 75–108 (2005); Ann. New York Acad. Sci. 1065, 346–374 (2006)]. It complicates both the Lagrange- and Delaunay-type planetary equations and makes the Delaunay equations
noncanonical. In attitude dynamics, whenever a perturbation depends upon the angular velocity (like a switch to a noninertial
frame), a mere amendment of the Hamiltonian makes the equations yield nonosculating Andoyer elements. To make them osculating,
extra terms should be added to the equations (but then the equations will no longer be canonical). Calculations in nonosculating
variables are mathematically valid, but their physical interpretation is not easy. Nonosculating orbital elements parameterise
instantaneous conics not tangent to the orbit. (A nonosculating i may differ much from the real inclination of the orbit, given by the osculating i.) Nonosculating Andoyer elements correctly describe perturbed attitude, but their interconnection with the angular velocity
is a nontrivial issue. The Kinoshita–Souchay theory tacitly employs nonosculating Andoyer elements. For this reason, even
though the elements are introduced in a precessing frame, they nevertheless return the inertial velocity, not the velocity
relative to the precessing frame. To amend the Kinoshita–Souchay theory, we derive the precessing-frame-related directional
angles of the angular velocity relative to the precessing frame. The loss of osculation should not necessarily be considered
a flaw of the Kinoshita–Souchay theory, because in some situations it is the inertial, not the relative, angular velocity
that is measurable [Schreiber, K. U. et al.: J. Geophys. Res. 109, B06405 (2004); Petrov, L.: Astron. Astrophys. 467, 359–369 (2007)]. Under these circumstances, the Kinoshita–Souchay formulae for the angular velocity should be employed (as
long as they are rightly identified as the formulae for the inertial angular velocity). 相似文献
16.
S.N. Pandey 《Astrophysics and Space Science》2001,277(3):403-408
A model of the universe based on Brans-Dicke theory with non-vanishing cosmological constant and non-zero curvature is studied.
Equations (13) and (16) have been obtained by the assumption f(t) = φ(t)a
3
(t),which give the values of the scale factor, a(t) and scalar field, φ(t) in terms of the observable parameters. Also, for a particular case of matter dominated universe, Equation (20) is obtained
which gives the relation between various parameters.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
El-Nabulsi Ahmad?Rami 《Astrophysics and Space Science》2011,332(2):491-495
We investigate the late-time dynamics of a four-dimensional universe based on modified scalar field gravity in which the standard
Einstein-Hilbert action R is replaced by f(φ)R+f(R) where f(φ)=φ
2 and f(R)=AR
2+BR
μν
R
μν,(A,B)∈ℝ. We discussed two independent cases: in the first model, the scalar field potential is quartic and for this special form
it was shown that the universe is dominated by dark energy with equation of state parameter w≈−0.2 and is accelerated in time with a scale factor evolving like a(t)∝t
5/3 and B+3A≈0.036. When, B+3A→∞ which corresponds for the purely quadratic theory, the scale factor evolves like a(t)∝t
1/2 whereas when B+3A→0 which corresponds for the purely scalar tensor theory we found when a(t)∝t
1.98. In the second model, we choose an exponential potential and we conjecture that the scalar curvature and the Hubble parameter
vary respectively like
R=hH[(f)\dot]/f,h ? \mathbbRR=\eta H\dot{\phi}/\phi,\eta\in\mathbb{R} and
H=g[(f)\dot]c,(g,c) ? \mathbbRH=\gamma\dot{\phi}^{\chi},(\gamma,\chi)\in\mathbb{R}. It was shown that for some special values of χ, the universe is free from the initial singularity, accelerated in time, dominated by dark or phantom energy whereas the
model is independent of the quadratic gravity corrections. Additional consequences are discussed. 相似文献
18.
A non-static exact solution of the Einstein equations corresponding to a conformally invariant scalar field with trace-free energy momentum tensor is obtained for the Robertson-Walker type metric. Some physical properties of the solution are discussed. 相似文献
19.
Emilio Santos 《Astrophysics and Space Science》2012,341(2):411-416
A gravity theory is considered with the Einstein-Hilbert Lagrangean R+aR 2+bR μν R μν , R μν being Ricci’s tensor and R the curvature scalar. The parameters a and b are taken of order 1 km2. Arguments are given which suggest that the effective theory so obtained might be a fair approximation of a viable theory. A numerical integration is performed of the field equations for a free neutron gas. The result is that the star mass increases with increasing central density until about 1 solar mass and then decreases. The baryon number increases monotonically, which suggests that the theory allows stars in equilibrium with arbitrary baryon number, no matter how large. 相似文献
20.
In this paper, we investigate the dynamics of Born–Infeld (B–I) phantom model in the ω–ω′ plane, which is defined by the equation of state parameter for the dark energy and its derivative with respect to N (the logarithm of the scale factor a). We find the scalar field equation of motion in ω–ω′ plane, and show mathematically the property of attractor solutions which correspond to ω
φ
∼−1, Ω
φ
=1, which avoid the “Big rip” problem and meets the current observations well.
相似文献