共查询到20条相似文献，搜索用时 46 毫秒
1.
《New Astronomy》2021
This study set out to examine the effect of anisotropy on the various dark energy models by using the observational data, including the Sandage-Loeb test, Strongly gravitationally lensing, observational Hubble data, and Baryon Acoustic Oscillations data. In particular, we consider three cases of dark energy models: the cosmological constant model, which is most favored by current observations, the wCDM model where dark energy is introduced with constant w equation of state parameter and in Chevalier-Polarski-Linder parametrization where ω is allowed to evolve with redshift. With an anisotropy framework, a maximum likelihood method to constrain the cosmological parameters was implemented. With an anisotropic universe, we also study the behavior of different cosmological parameters such as Hubble parameter, EoS parameter, and deceleration parameter of dark energy models mentioned. The results indicate that the Bianchi type I model for the dark energy models are consistent with the combined observational data. 相似文献
2.
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
3.
S. K. Tripathy S. K. Nayak S. K. Sahu T. R. Routray 《Astrophysics and Space Science》2009,323(1):91-96
Bianchi type-I string cosmological models are studied in Saez-Ballester theory of gravitation when the source for the energy
momentum tensor is a viscous string cloud coupled to gravitational field. The bulk viscosity is assumed to vary with time
and is related to the scalar expansion. The relationship between the proper energy density ρ and string tension density λ are investigated from two different cosmological models. 相似文献
4.
The present study deals with spatially homogeneous and anisotropic locally rotationally symmetric (LRS) Bianchi type I cosmological
model with dominance of dark energy. To get the deterministic model of Universe, we assume that the shear scalar (σ) in the model is proportional to expansion scalar (θ). This condition leads to A=B
n
, where A, B are metric potential and n is positive constant. It has been found that the anisotropic distribution of dark energy leads to the present accelerated
expansion of Universe. The physical behavior of the Universe has been discussed in detail. 相似文献
5.
The scaling of the apparent angular diameter of galaxies with redshift θ(z) is a powerful discriminator of cosmological models. In this paper we argue that the rotational velocity of distant galaxies, when interpreted as size indicator, may be used as an interesting tool to select high redshift standard rods. Upcoming deep redshift surveys will allow an implementation of this classical geometrical test to measure directly the amplitude of the cosmological constant Λ, or to constrain the cosmic equation of state parameter for a smooth dark energy component (w = p/ρ, —1 ≤ w < 0). 相似文献
6.
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
7.
M. R. Setare 《Astrophysics and Space Science》2010,326(1):27-31
In this paper, we study a cosmological application of the new agegraphic dark energy density in the f(R) gravity framework. We employ the new agegraphic model of dark energy to obtain the equation of state for the new agegraphic
energy density in a spatially flat universe. Our calculations show, taking n<0, that it is possible to have w
Λ crossing −1. This implies that one can generate a phantom-like equation of state from a new agegraphic dark energy model
in a flat universe in the modified gravity cosmology framework. Also, we develop a reconstruction scheme for the modified
gravity with f(R) action. 相似文献
8.
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
9.
V. Fayaz H. Hossienkhani A. Farmany M. Amirabadi N. Azimi 《Astrophysics and Space Science》2014,351(1):299-306
It is shown that the acceleration of the universe can be understood by considering a f(T) gravity models. Modified teleparallel gravity theory with the torsion scalar has recently gained a lot of attention as a possible explanation of dark energy. For these f(T) gravity models, a variant of the accelerating cosmology reconstruction program is developed. We consider spatially homogenous and anisotropic Bianchi type I universe in the context of f(T) gravity. The de Sitter, power-law and general exponential solutions are assumed for the scale factor in each spatial direction and the corresponding cosmological models are reconstructed. We reconstruct f(T) theories from two different holographic dark energy models in different time durations. For the holographic dark energy model, the dark energy dominated era with new setting up is chosen for reconstruction, and the Ricci dark energy model, radiation, matter and dark energy dominated time durations are all investigated. Finally we have obtained a modified gravity action consistent with the holographic dark energy scenario. 相似文献
10.
We explore the predictions of a class of dark energy models, quinstant dark energy, concerning the structure formation in
the Universe, both in the linear and non-linear regimes. Quinstant dark energy is considered to be formed by quintessence and a negative cosmological constant. We conclude that these models give good predictions for structure formation in the linear regime, but fail to do so in the
non-linear one, for redshifts larger than one. 相似文献
11.
12.
《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
13.
We investigate the anisotropic locally rotationally symmetric (LRS) Bianchi type I cosmological model with dark matter and anisotropic dark energy. We assume that the shear scalar \((\sigma )\) is proportional to expansion scalar \((\theta )\). A special law is introduced for two skewness parameters that describe the deviation of pressure from isotropy. This law can lead to models: the hybrid expansion, the big rip and the little rip. The behavior of the Universe is discussed depending on the numerical parameters of the models. 相似文献
14.
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
15.
16.
Kantowski-Sachs cosmological model in the presence of magnetized anisotropic dark energy is investigated. The energy-momentum
tensor consists of anisotropic fluid with anisotropic EoS p=ωρ and a uniform magnetic field of energy density ρ
B
. We obtain exact solutions to the field equations using the condition that expansion is proportional to the shear scalar.
The physical behavior of the model is discussed with and without magnetic field. We conclude that universe model as well as
anisotropic fluid does not approach isotropy through the evolution of the universe. 相似文献
17.
Arbab I. Arbab 《Astrophysics and Space Science》2004,291(2):143-149
We have shown that the phenomenological models with a cosmological constant of the type Λ=β(
) and Λ=3αH
2, where R is the scale factor of the universe and H is the Hubble constant, are equivalent to a quintessence model with a scalar (φ) potential of the formV∝φ-n, n= constant. The equation of state of the cosmic fluid is described by these parameters (α, β, n) only. The equation of state of the cosmic fluid (dark energy) can be determined by any of these parameters. The actual amount of dark energy will define the equation of state of the cosmic fluid.All of the three forms can give rise to cosmic acceleration depending the amount of dark energy in the universe. 相似文献
18.
Artyom V. Astashenok 《Astrophysics and Space Science》2014,351(1):377-383
Various cosmological models in frames of F(T) gravity are considered. The general scheme of constructing effective dark energy models with various evolution is presented. It is showed that these models in principle are compatible with ΛCDM model. The dynamics of universe governed by F(T) gravity can mimics ΛCDM evolution in past but declines from it in a future. We also construct some dark energy models with the “real” (non-effective) equation-of-state parameter w such that w≤?1. It is showed that in F(T) gravity the Universe filled phantom field not necessarily ends its existence in singularity. There are two possible mechanisms permitting the final singularity. Firstly due to the nonlinear dependence between energy density and H 2 (H is the Hubble parameter) the universe can expands not so fast as in the general relativity and in fact Little Rip regime take place instead Big Rip. We also considered the models with possible bounce in future. In these models the universe expansion can mimics the dynamics with future singularity but due to bounce in future universe begin contracts. 相似文献
19.
《New Astronomy》2021
This article is concerned with the investigation of dynamical behaviour of Kaluza-Klein(KK) FRW type dark energy cosmological models in the framework of a scalar-tensor theory of gravitation formulated by Saez and Ballester (Phys. Lett. A113,467:1986). Three cosmological models, in this theory, are presented by solving the field equations using (i) hybrid expansion law given by Pradhan et al. (Ind.J.Phys.89,5032015), (ii)varying deceleration parameter proposed by Mishra et al.(Int. J. Theor. Phy.52, 2546: 2013) and(iii)linearly varying deceleration parameter defined by Akarsu and Dereli (Int. J. Theor. Phys. 51, 612: 2012). We have evaluated the dynamical parameters for each of the models, namely, the equation of state (EoS) parameter, the deceleration parameter, statefinder parameter and total energy density parameter of dark energy. We have also found the scalar field in the models. We have discussed the dynamical behavior of the parameters through graphical representation with special reference to Planck Collaboration data. It is observed that our models describe accelerated expansion of the universe and our theoretical results are, reasonably, in good agreement with the observational data. 相似文献
20.
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