共查询到20条相似文献，搜索用时 31 毫秒
1.
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
2.
F. Rahaman S. Chakraborty S. Das R. Mukherjee M. Hossain N. Begam 《Astrophysics and Space Science》2003,288(4):379-387
We have presented in homogeneous cosmological models within the framework of Lyra geometry. We have considered an inhomogeneous
spherically symmetric higher dimensional model in presence of a mass less scalar field whose potential has a flat part. The
scalar field is considered to be inhomogeneous. Also an inhomogeneous cosmological model is derived in a Kaluza-Klein type
of space time. The matter field is taken as an inhomogeneous distribution of fluid. It is observed that there is no singularity
at finite past in our model and the desirable feature of dimensional reduction is also possible for the extra space.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
3.
We consider a cosmological model in which a scalar field is non-minimally coupled to scalar torsion and a vector field through two coupling functions in the framework of teleparallel gravity. The explicit forms of the coupling functions and the scalar field potential are explored, under the assumption that the Lagrangian admits the Noether symmetry in the Friedmann–Lemaître–Robertson–Walker (FLRW) space–time. The existence of such symmetry allows to solve the equations of motion and achieve exact solutions of the scale factor, scalar and vector fields. It is found that the vector field contributes significantly in the accelerating expansion of the universe in the early times, while the scalar field plays an essential role in the late times. 相似文献
4.
We consider the BSBM(Bekenstein, Sandvik, Barrow and Magueijo) cosmological model in the presence of tachyon potential with the aim of studying the stability of the model and test it against observations. The phase space analysis shows that from fourteen critical points that represent the state of the universe, only one is stable.With a small perturbation, the universe transits from a state of unstable deceleration to stable acceleration. The stability analysis combined with the best fitting process imposes constraints on the cosmological parameters that are in agreement with observation. In the BSBM theory, the variation of fundamental constants is driven from variation of a scalar field. The tachyonic scalar field, responsible for both variation of fundamental constants and universal acceleration, is reconstructed. 相似文献
5.
An exact cosmological solution for Friedman Robertson Walker (FRW)metric is obtained with a classical scalar field φ along
with a potential in the presence of a causal viscous fluid. Assuming the scale factor to be a function of the scalar field
we have obtained solutions in both the truncated and the full causal theory. It is shown that an inflationary model can be
obtained by imposing certain constraints on some constants. The radiative bulk viscosity during the decoupling era has also
been studied as a special case.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
6.
In this paper, we have investigated the inflationary Kantowski-Sachs cosmological model in the presence of mass less scalar
field with a flat potential. To get an inflationary solution, we have considered a flat region of a constant potential V. Some physical and kinematical properties of the model are studied. 相似文献
7.
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
8.
A. A. Saaryan 《Astrophysics》1995,38(1):55-67
The low-energy string gravitation is investigated for the case of reduction with a variable (in string units) inner space. A flat cosmological model of the corresponding four-dimensional theory is constructed. The model equations are analyzed qualitatively for a potential-dominated scalar field as the source. It is demonstrated that an extended inflation stage with one purely scalar dilaton field is possible here, in contrast with the case of a constant inner space. The pattern of cosmological evolution in various conformal representations is discussed.Translated from Astrofizika, Vol. 38, No. 1, pp. 99–119, January–March, 1995. 相似文献
9.
M. N. Varma 《Astrophysics and Space Science》1989,161(1):181-184
A spatially flat Robertson-Walker R-W cosmological model filled with a massive scalar field has been obtained for Einstein's field equations in the presence of a cosmological constant. 相似文献
10.
We consider cosmological dynamics of a canonical bulk scalar field, which is coupled non-minimally to 5-dimensional Ricci scalar in a DGP setup. We show that presence of this non-minimally coupled bulk scalar field affects the jump conditions of the original DGP model significantly. Within a superpotential approach, we perform some numerical analysis of the model parameter space and consider bulk-brane energy exchange in this setup. Also we show that the normal, ghost-free branch of the DGP solutions in this case has the potential to realize a self-consistent phantom-like behavior and therefore explains late time acceleration of the universe in a consistent way. 相似文献
11.
《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
12.
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
13.
In this work we present a phase-space analysis of the cosmological relaxation of generalized gravity theories where the gravitational
constant G varies towards general relativity. We assess the interplay of the two main mechanisms that yield general relativity
as the cosmological attractor: (i) the vanishing of the coupling function α(ϕ), and (ii) the existence of a minimum of the
scalar field potential. The latter mechanism is shown to supersede the first. We classify the fixed points associated to different
types of potentials and discuss the late time self-similar solutions that arise when the scalar field potential exhibits an
asymptotic exponential behaviour from the viewpoint of the relaxation mechanism.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
Homogeneous isotropic cosmological solutions are obtained for a de Sitter type of metric in the presence of a self-gravitating scalar field with cubic nonlinearity. Unlike the usual de Sitter case which is indefinitely expanding it is here interestingly found that in the presence of a nonlinear scalar field the model gives a bounce from a maximum of spatial volume. The possibility of bounce from a maximum, however, disappears when a linear scalar field is considered instead. 相似文献
15.
Farook Rahaman Subenoy Chakraborty Jayanta Kr. Bera 《Astrophysics and Space Science》2002,281(3):595-600
The inhomogeneous Bianchi-I model based on Lyra's geometry has been studied in the cosmological theory in presence of a massless
inhomogeneous scalar field whose potential has a flat part. The field equations are solved using separation of variables and
it is shown that one of the time part of the field equations are solvable for any arbitrary other cosmic scale function. Solutions
for a particular form of cosmic scale (time part) is presented.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
16.
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
17.
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
18.
We reconsider the issue of cosmological dynamics in a DGP setup with a bulk scalar field. The ghost-free, normal branch of
this DGP-inspired braneworld scenario has the potential to realize a self-consistent phantom-like behavior. The roles played
by the bulk canonical scalar field on this phantom-like dynamics are explored. Within a dynamical system approach, the effective
phantom nature of the scenario is investigated with details. This analysis shows that there is a stable, late-time de Sitter
phase. 相似文献
19.
Yousef Bisabr 《Astrophysics and Space Science》2014,350(1):407-411
We consider a generalized Brans-Dicke model in which the scalar field has a potential function and is also allowed to couple non-minimally with the matter sector. This anomalous gravitational coupling can in principle avoid the model to pass local gravity experiments. One then usually assumes that the scalar field has a chameleon behavior in the sense that it acquires a density-dependent effective mass. While it can take a small effective mass in cosmological (low-density environment) scale, it has a sufficiently heavy mass in Solar System (large-density environment) and then hides gravity tests. We will argue that such a chameleon behavior can not be generally realized and depends significantly on the forms attributed to the potential and the coupling functions. 相似文献
20.
Ashok KR. Chakraborty 《Astrophysics and Space Science》1992,192(2):321-324
In this Letter the five-dimensional Kaluza-Klein cosmological model is studied in the presence of a massless scalar field, whose potential has a flat part. By use of the polynomial relation between the two scale factors, inflationary solutions are obtained. The results show that the scale factor corresponding to the extra dimension is either constant or varies inversely as some power of the usual scale factor. 相似文献