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The paper is devoted to an investigation of the relationships between the classical Friedmann cosmology and the Dirac Hamiltonian
approach to quantization of the universe, based on the simple but important example of a homogeneous universe filled with
excitations of a scalar field. The method of gaugeless reduction is used to completely separate the sector of physical variables
from the purely gauge sector, making it possible to find the relationship between cosmological observables in the Friedmann
— Einstein sense and observables of the Dirac Hamiltonian formalism in the Narlikar conformai reference frame. Gaugeless reduction
enabled us to establish that in the process of reduction, one of the variables of the nonphysical sector is converted into
an invariant time parameter and cannot be treated as a dynamical variable in either the functional or the operator approach
to quantization. It is shown that in this conversion of a variable into a time parameter, the Hartle-Hawking functional integral
is the reason why the wave function of the Wheeler—De Witt (WDW) equation cannot be normalized and why an infinite gauge factor
arises. The gaugeless reduction provides a certain recipe for mathematical and physical interpretation of the WDW equation
and wave functions, the use of which makes their relationship to observational cosmology clear and transparent. It is shown,
in particular, how the WDW wave function describes the Friedmann evolution with respect to proper time.
Translated from Astrofizika, Vol. 40, No. 2, pp. 303–321, April–June, 1997. 相似文献
3.
F. Darabi 《Astrophysics and Space Science》2012,338(1):171-177
We study a gravitational model in which scale transformations play the key role in obtaining dynamical G and Λ. We take a non-scale invariant gravitational action with a cosmological constant and a gravitational coupling constant.
Then, by a scale transformation, through a dilaton field, we obtain a new action containing cosmological and gravitational
coupling terms which are dynamically dependent on the dilaton field with Higgs type potential. The vacuum expectation value
of this dilaton field, through spontaneous symmetry breaking on the basis of anthropic principle, determines the time variations of G and Λ. The relevance of these time variations to the current acceleration of the universe, coincidence problem, Mach’s cosmological
coincidence and those problems of standard cosmology addressed by inflationary models, are discussed. The current acceleration
of the universe is shown to be a result of phase transition from radiation toward matter dominated eras. No real coincidence
problem between matter and vacuum energy densities exists in this model and this apparent coincidence together with Mach’s
cosmological coincidence are shown to be simple consequences of a new kind of scale factor dependence of the energy momentum
density as ρ∼a
−4. This model also provides the possibility for a super fast expansion of the scale factor at very early universe by introducing
exotic type matter like cosmic strings. 相似文献
4.
There is a growing interest among cosmologists for theories with negative energy scalar fields and creation, in order to model
a repulsive gravity. The classical steady state cosmology proposed by Bondi, Gold & Hoyle in 1948, was the first such theory
which used a negative kinetic energy creation field to invoke creation of matter. We emphasize that creation plays a very
crucial role in cosmology and provides a natural explanation to the various explosive phenomena occurring in local (z < 0.1) and extra galactic universe. We exemplify this point of view by considering the resurrected version of this theory
— the quasi-steady state theory, which tries to relate creation events directly to the large scale dynamics of the universe
and supplies more natural explanations of the observed phenomena.
Although the theory predicts a decelerating universe at the present era, it explains successfully the recent SNe Ia observations
(which require an accelerating universe in the standard cosmology), as we show in this paper by performing a Bayesian analysis
of the data. 相似文献
5.
Martin J. Rees 《Journal of Astrophysics and Astronomy》1984,5(4):331-348
The evidence for unseen mass (which is briefly reviewed) suggests that the cosmological density parameter Ω is at least 0.1–0.2.
An Einstein-de-Sitter ‘flat’ universe with Ω = 1 — which is appealing for theoretical reasons — can only be reconciled with
the data if the galaxies are more ‘clumped’ than the overall mass distribution, and are poor tracers of the unseen mass even
on scales of several Mpc. Possible forms for the unseen mass are discussed; and feedback processes are outlined whereby galaxy
formation can be suppressed in underdense regions. 相似文献
6.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2010,327(2):161-165
We investigate the cosmological dynamics of a four-dimensional Friedmann–Robertson–Walker homogenous and isotropic universe
from Gauss–Bonnet higher-order curvature corrections, together with nonminimal coupling and with an infrared effective action
of gravity based on a second-order gauge formulation for the Lorentz group. We study the evolution of the universe in such
a model, identifying its key properties. Many new interesting features are revealed and discussed in some detail. 相似文献
7.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2009,324(1):71-75
The recent observational available data for an accelerated expansion state of the present universe, obtained from distant
SNeIa gave strong support to the search of alternative cosmologies. Recently, there have been a number of different attempts
to modify Einstein’s gravity to yield accelerated expansion at late times. Unfortunately, many of the theoretical models discussed
in the literature are plagued with theoretical problems, in particular the singularity problem at the origin of time. In the
present work we have analyzed a multidimensional spacetime Friedmann–Robertson–Walker (FRW) model with a decaying cosmological
constant and a varying gravitational constant. Many interesting consequences are revealed, in particular the behavior of the
scale factor and the shape of the universe in terms of the number of extra dimensions. 相似文献
8.
In part I we suggested an approximate equation to determine the contribution of relativistic effects to the moment of inertia
of a superdense star. In the present paper it is tested on model neutron stars with nine different variants of the equation
of state of superdense matter. It is established that the approximation error does not exceed 5% for stable configurations.
A more accurate version of the Ravenhall—Pethick equation [D. G. Ravenhall and C. J. Pethick, Astrophys. J., 424, 846 (1994)]
for the moment of inertia as a function of the mass and radius of a neutron star is derived.
Translated from Astrofizika, Vol. 40, No. 4, pp. 507–516, October–December, 1997. 相似文献
9.
The recently discovered accelerated expansion of the universe is of current interest in theoretical research on the evolution
of the universe. The cause of this behavior is presumably the presence of dark energy, which has been estimated to form up
to 70% of the universe and generates a “repulsive force.” In this paper a cosmological model is constructed which takes the
dark energy into account in a Jordan-Brans-Dicke tensor-scalar model with a dominant, nonminimally coupled scalar field in
the presence of a cosmological scalar. The radiation dominant epoch is discussed.
__________
Translated from Astrofizika, Vol. 51, No. 1, pp. 151–159 (February 2008). 相似文献
10.
Yuan Ren Pierpaolo Pergola Elena Fantino Bianca Thiere 《Celestial Mechanics and Dynamical Astronomy》2012,112(1):1-21
Over the past three decades, ballistic and impulsive trajectories between libration point orbits (LPOs) in the Sun–Earth–Moon
system have been investigated to a large extent. It is known that coupling invariant manifolds of LPOs of two different circular
restricted three-body problems (i.e., the Sun–Earth and the Earth–Moon systems) can lead to significant mass savings in specific
transfers, such as from a low Earth orbit to the Moon’s vicinity. Previous investigations on this issue mainly considered
the use of impulsive maneuvers along the trajectory. Here we investigate the dynamical effects of replacing impulsive ΔV’s with low-thrust trajectory arcs to connect LPOs using invariant manifold dynamics. Our investigation shows that the use
of low-thrust propulsion in a particular phase of the transfer and the adoption of a more realistic Sun–Earth–Moon four-body
model can provide better and more propellant-efficient solution. For this purpose, methods have been developed to compute
the invariant tori and their manifolds in this dynamical model. 相似文献
11.
Using the teleparallel gravity versions of the Einstein and Landau–Lifshitz’s energy and/or momentum complexes, I obtain the
energy and momentum of the universe in viscous Kasner-type cosmological models. The energy and momentum components (due to
matter plus field) are found to be zero and this agree with a previous work of Rosen and Johri et al., who investigated the
problem of the energy in Friedmann–Robertson–Walker (FRW) universe. The result that the total energy and momentum components
of the universe in these models is zero same as Bergmann–Thomson’s energy–momentum and props the viewpoint of Tryon. Rosen
found that the energy of the FRW space–time is zero, which agrees with the studies of Tryon.
PACs Numbers: 04.20.-q; 04.50.+h
An erratum to this article is available at . 相似文献
12.
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
13.
A spatially homogeneous and isotropic Robertson-Walker model with zero-curvature of the universe is studied in Saez-Ballester
scalar-tensor theory. Exact solutions of the field equations are obtained for two different early phases of the universe viz.
the inflationary and the radiation-dominated phases by using gamma-law equation of state p=(γ-1)ρ in the presence of perfect fluid. The γ-index describing the material content varies continuously with cosmic time
so that in the course of its evolution, the universe goes through a transition from an inflationary phase to a radiation-dominated
phase. The coupling parameterω is allowed to depend on the cosmic time. The nature of scalar field and other physical significance
have also been discussed.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
We propose in this paper an interacting holographic dark energy (IHDE) model in chameleon–tachyon cosmology by interaction
between the components of the dark sectors. In the formalism, the interaction term emerges from the scalar field coupling
matter Lagrangian in the model rather than being inserted into the formalism as an external source for the interaction. The
correspondence between the tachyon field and the holographic dark energy (HDE) densities allows to reconstruct the tachyon
scalar field and its potential in a flat FRW universe. The model can show the accelerated expansion of the universe and satisfies
the observational data. 相似文献
15.
Jayant V. Narlikar Geoffrey Burbidge R. G. Vishwakarma 《Journal of Astrophysics and Astronomy》2007,28(2-3):67-99
In this paper we discuss the properties of the quasi-steady state cosmological model (QSSC) developed in 1993 in its role
as a cyclic model of the universe driven by a negative energy scalar field. We discuss the origin of such a scalar field in
the primary creation process first described by F. Hoyle & J. V. Narlikar forty years ago. It is shown that the creation processes
which take place in the nuclei of galaxies are closely linked to the high energy and explosive phenomena, which are commonly
observed in galaxies at all redshifts.
The cyclic nature of the universe provides a natural link between the places of origin of the microwave background radiation
(arising in hydrogen burning in stars), and the origin of the lightest nuclei (H, D, He3 and He4). It also allows us to relate the large scale cyclic properties of the universe to events taking place in the nuclei of galaxies.
Observational evidence shows that ejection of matter and energy from these centers in the form of compact objects, gas and
relativistic particles is responsible for the population of quasi-stellar objects (QSOs) and gamma-ray burst sources in the
universe.
In the later parts of the paper we briefly discuss the major unsolved problems of this integrated cosmological and cosmogonical
scheme — the understanding of the origin of the intrinsic redshifts, and the periodicities in the redshift distribution of
the QSOs. 相似文献
16.
The importance of the stability characteristics of the planar elliptic restricted three-body problem is that they offer insight
about the general dynamical mechanisms causing instability in celestial mechanics. To analyze these concerns, elliptic–elliptic
and hyperbolic–elliptic resonance orbits (periodic solutions with lower period) are numerically discovered by use of Newton's
differential correction method. We find indications of stability for the elliptic–elliptic resonance orbits because slightly
perturbed orbits define a corresponding two-dimensional invariant manifold on the Poincaré surface-section. For the resonance
orbit of the hyperbolic–elliptic type, we show numerically that its stable and unstable manifolds intersect transversally
in phase-space to induce instability. Then, we find indications that there are orbits which jump from one resonance zone to
the next before escaping to infinity. This phenomenon is related to the so-called Arnold diffusion.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
17.
We study the motion of an infinitesimal mass point under the gravitational action of three mass points of masses μ, 1–2μ and
μ moving under Newton's gravitational law in circular periodic orbits around their center of masses. The three point masses
form at any time a collinear central configuration. The body of mass 1–2μ is located at the center of mass. The paper has
two main goals. First, to prove the existence of four transversal ejection–collision orbits, and second to show the existence
of an uncountable number of invariant punctured tori. Both results are for a given large value of the Jacobi constant and
for an arbitrary value of the mass parameter 0<μ≤1/2.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
18.
In this paper we have investigated the effect of magnetic field on an orthogonal Bianchi type-I inflationary cosmological
model using the concept of Higgs field. It has been investigated that the expansion and inflation in the model increases as
the magnetic field increases. To get inflationary model we have assumed a mass less scalar field with flat potential V(φ)that has flat region.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
19.
M. Malekjani A. Khodam-Mohammadi N. Nazari-pooya 《Astrophysics and Space Science》2011,334(1):193-201
The generalized Chaplygin gas (GCG) model in spatially flat universe is investigated. The cosmological consequences led by
GCG model including the evolution of EoS parameter, deceleration parameter and dimensionless Hubble parameter are calculated.
We show that the GCG model behaves as a general quintessence model. The GCG model can also represent the pressureless CDM
model at the early time and cosmological constant model at the late time. The dependency of transition from decelerated expansion
to accelerated expansion on the parameters of model is investigated. The statefinder parameters r and s in this model are derived and the evolutionary trajectories in s–r plane are plotted. Finally, based on current observational data, we plot the evolutionary trajectories in s–r and q–r planes for best fit values of the parameters of GCG model. It has been shown that although, there are similarities between
GCG model and other forms of Chaplygin gas in statefinder plane, but the distance of this model from the ΛCDM fixed point
in s–r diagram is shorter compare with standard Chaplygin gas model. 相似文献
20.
BOEHNHARDT H. BIRKLE K. FIEDLER A. JORDA L. THOMAS N. PESCHKE S. RAUER H. SCHULZ R. SCHWEHM G. TOZZI G. WEST R. 《Earth, Moon, and Planets》1997,78(1-3):179-187
In 1996 comet Hale-Bopp exhibited a porcupine-like coma with straight jets of dust emission from several active regions on
the nucleus. The multi-jet coma geometry developed during the first half of 1996. While the jet orientation remained almost
constant over months, the relative intensity of the jets changed with time. By using the embedded fan model of Sekanina and
Boehnhardt (1997a) the jet pattern of comet Hale-Bopp in 1996 can be interpreted as boundaries of dust emission cones (fans)
from four — possibly five — active regions on the nucleus (for a numerical modelling see part II of the paper by Sekanina
and Boehnhardt, 1997b).
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献