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1.
Cosmological solutions are examined in the proper representation of the JBD theory with a dominant nonminimally coupled scalar
field. It is shown that only the introduction of a cosmological scalar that transforms to the ordinary cosmological constant
in the Einstein representation enables a phase of evolution with a uniform and then an accelerated expansion of the universe
over cosmological time scales.
__________
Translated from Astrofizika, Vol. 48, No. 4, pp. 633–640 (November 2005). 相似文献
2.
《New Astronomy》2021
Investigation of dark energy models in the presence of scalar fields are attracting several kinds of research because they play a vital role in the discussion of a new scenario of accelerated expansion of the universe. In this paper, we obtain an exact plane-symmetric dark energy cosmological model in the presence of an attractive massive scalar field by solving Einstein field equations using some physically relevant conditions. We have obtained all the cosmological parameters corresponding to the model. We have also presented a physical discussion of our model using a graphical representation of these parameters. The results exhibit an expanding and accelerating dark energy model of the universe, which are consistent with modern cosmological observations. 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.
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.
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Translated from Astrofizika, Vol. 49, No. 3, pp. 487–498 (August 2006). 相似文献
5.
In this paper, we investigate Bianchi type-VI cosmological model for the universe filled with dark energy and viscous fluid in the presence of cosmological constant. Also, we show accelerating expansion of the universe by drawing volume scale, pressure and energy density versus cosmic time. In order to solve the Einstein’s field equations, we assume the expansion scalar is proportional to a component of the shear tensor. Therefore, we obtain the directional scale factors and show the EOS parameter crosses over phantom divided-line. 相似文献
6.
Farkhat Zaripov 《Astrophysics and Space Science》2014,352(1):289-305
This research is an extension of the author’s works, in which conformally invariant generalization of string theory was suggested to higher-dimensional objects. Special cases of the proposed theory are Einstein’s theory of gravity and string theory. This work is devoted to the formation of self-consistent equations of the theory of induced gravity in the presence of matter in the form of a perfect fluid that interacts with scalar fields. The study is done to solve these equations for the case of the cosmological model. In this model time-evolving gravitational and cosmological “constants” take place which are determined by the square of scalar fields. The values of which can be matched with the observational data. The equations that describe the theory have solutions that can both match with the solutions of the standard theory of gravity as well as it can differ from it. This is due to the fact that the fundamental “constants” of the theory, such as gravitational and cosmological, can evolve over time and also depend of the coordinates. Thus, in a rather general case the theory describes the two systems (stages): Einstein and “evolving”. This process is similar to the phenomenon of phase transition, where the different phases (Einstein gravity system, but with different constants) transit into each other. 相似文献
7.
We look for cosmologies with a scalar field (dark energy without cosmological constant), which mimic the standard ΛCDM cosmological
model yielding exactly the same large-scale geometry described by the evolution of the Hubble parameter (i.e. photometric
distance and angular diameter distance as functions on z). Asymptotic behavior of the field solutions is studied in the case of spatially flat Universe with pressureless matter and
separable scalar field Lagrangians; the cases of power-law kinetic term and power-law potential are considered. Exact analytic
solutions are found in some special cases. A number of models have the field solutions with infinite behavior in the past
or even singular behavior at finite redshifts. We point out that introduction of the cosmological scalar field involves some
degeneracy leading to lower precision in determination of Ω
m
. To remove this degeneracy additional information is needed besides the data on large-scale geometry.
The article is published in the original. 相似文献
8.
Sanjay Sarkar 《Astrophysics and Space Science》2014,350(2):821-829
In this work, we have considered the spatially homogeneous and anisotropic Bianchi type-II universe filled with two interacting fluids; dark matter and holographic dark energy components. Assuming the proportionality relation between one of the components of shear scalar and expansion scalar which yields time dependent deceleration parameter, an exact solution to Einstein’s field equations in Bianchi type-II line element is obtained. We have investigated geometric and kinematics properties of the model and the behaviour of the holographic dark energy. It is observed that the mean anisotropic parameter is uniform through the whole evolution of the universe and the coincidence parameter increases with increasing time. The solutions are also found to be in good agreement with the results of recent observations. We have applied the statefinder diagnostics method to study the behaviour of different stages of the universe and to differentiate the proposed dark energy model from the ΛCDM model. We have also established a correspondence between the holographic dark energy model and the tachyon scalar field dark energy model. We have reconstructed the potential and the dynamics of the tachyon scalar field, which describes accelerated expansion of the universe. 相似文献
9.
M. D. Roberts 《Astrophysics and Space Science》1993,200(2):331-335
It is known that the requirement of asymptotic flatness places restrictions on spherically-symmetric solutions to field equations. Here it is shown that the most general solution to the static spherically-symmetric massless scalar Einstein equations with zero cosmological constant is asymptotically flat; furthermore, the general solution is derived and shown to be identical to a solution previusly found by M. Wyman. 相似文献
10.
《New Astronomy》2019
We have constructed a model in Lyra manifold and time varying cosmological constant with perfect fluid using LVDP (Linear Varying Deceleration Parameter). Bianchi type-III metric is used as source of investigation. To get a deterministic solution of the field equation the expansion scalar (θ) is considered as proportional to the shear scalar (σ). The cosmological constant is found to be positive which satisfies the result obtained by supernova Type-Ia Observations [1999]. Here we analyse the behaviour of pressure and deceleration parameter by using different form of dark energy(DE). In addition to it, some physical and geometrical properties of the solutions are studied. 相似文献
11.
In this paper, we solve the Einstein’s field equations for the space-time described by a special plane symmetric metric with
dark energy, and the exact solutions which offer an alternative and complementary approach to study cosmological models are
obtained. The dark energy is given by either the quintessence or the modified Chaplygin gas. We show the models are isotropic
and analyze the expansion scalar and the deceleration parameter of the models. 相似文献
12.
Metod Saniga 《Astrophysics and Space Science》1992,193(1):155-159
A U(1)-symmetric Yang-Mills-Higgs (i.e., an Abelian Higgs) sunspot's model is recognized to originate from a massless, complex-valued scalar field coupled minimally to electromagnetic gauge potentials in the background of a (globally)conformally symmetric semi-metric spacetime, whose metric structure is described by the generalized Einstein equations with nonvanishing (positive-valued) cosmological constant. It is shown, in particular, that non-linearity (selfcoupling) of the scalar field appears due to a non-zeroness of the cosmological term, whereas its non-zero vacuum amplitude is induced by the (Ricci scalar) curvature of the Sun's spacetime manifold. 相似文献
13.
We consider Brans-Dicke theory with a self-interacting potential in Einstein conformal frame. We introduce a class of solutions
in which an accelerating expansion is possible in a spatially flat universe for positive and large values of the Brans-Dicke
parameter consistent with local gravity experiments. In this Einstein frame formulation, the theory appears as an interacting
quintessence model in which the interaction term is given by the conformal transformation. In such an interacting model, we
shall show that the solutions lead simultaneously to a constant ratio of energy densities of matter and the scalar field. 相似文献
14.
《New Astronomy》2022
In the present investigation we are mainly concerned with a massive scalar field in an axially symmetric Bianchi type – I space-time. Einstein field equations are solved to obtain an exact cosmological model. We have used certain physically meaningful conditions for this purpose. Kinematical cosmological parameters are determined, and their dynamical aspects are discussed. It is observed that our model represents accelerated expansion of the Universe. It is observed that our model agrees with the scenario of accelerated expansion of the Universe confirmed by supernova 1a experimental data. 相似文献
15.
Various representations of the Jordan-Brans-Dicke (JBD) theory arising in conformal transformations of the metric are considered. Propositions are formulated that establish the mathematical equivalence of these representations, making it possible from known exact solutions in one representation to generate new ones in another. It is shown, in particular, how to obtain new solutions in the general theory of relativity from known solutions in the JBD theory and vice versa. 相似文献
16.
Exact solutions of the semi-classical Einstein equations for conformally invariant free quantum fields in an homogeneous and
isotropic space-time, with cosmological constant and containing a classical scalar field, dust matter, an unquantised Dirac
field and electromagnetic radiation are found. The initial behaviour of the semiclassical models is investigated. Some of
the solutions found avoid the singularity and do not have particle horizons.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
17.
Using a static massive spherically symmetric scalar field coupled to gravity in the Schwarzschild-de Sitter (SdS) background, first we consider some asymptotic solutions near horizon and their local equations of state (E.O.S.) on them. We show that near cosmological and event horizons our scalar field behaves as a dust. At the next step near two pure de Sitter or Schwarzschild horizons we obtain a coupling dependent pressure to energy density ratio. In the case of a minimally coupling this ratio is ?1 which springs to the mind thermodynamical behavior of dark energy. If having a negative pressure behavior near these horizons we concluded that the coupling constant must be ξ<¼. Therefore we derive a new constraint on the value of our coupling ξ. These two different behaviors of unique matter in the distinct regions of spacetime at present era can be interpreted as a phase transition from dark matter to dark energy in the cosmic scales and construct a unified scenario. 相似文献
18.
The solutions of Einstein’s equations with cosmological constant (Λ) in the presence of a creation field have been obtained for general class of anisotropic cosmological models. We have obtained the cosmological solutions for two different scenarios of average scale factor. In first case, we have discussed three different types of physically viable cosmological solutions of average scale factor for the general class of Bianchi cosmological models by using a special law for deceleration parameter which is linear in time with a negative slope. In second case, we have discussed another three different forms of cosmological solutions by using the average scale factor in three different scenarios like Intermediate scenario, Logamediate scenario and Emergent scenario. All physical parameters are calculated and discussed in each physical viable cosmological model. We examine the nature of creation field and cosmological constant is dominated the early Universe but they do not survive for long time and finally tends to zero for large cosmic time t. We have also discussed the all energy conditions in each cases. 相似文献
19.
Both Jordan–Brans–Dicke (shortened JBD) theory and Brans–Dicke theory in the Einstein’s frame (shortened EBD) are treated
as Brans–Dicke theory. However, we learn that only Pauli metric represents the massless spin-two graviton and thus, should
be identified as physical. If one just considers the weak field approximation and Newtonian limit, EBD theory gives the same
results with Einstein’s general relativity. So, it is necessary to consider strong field effects and cosmological model. The
purpose of this paper is to find the exact spherically symmetric metric in the strong field situation, and deduce the deviation
of light path in EBD theory. 相似文献