共查询到20条相似文献，搜索用时 46 毫秒
1.
Based on a new geometric diagnostic method-Om, we consider a new independent-model parametrization . When we work in potential W σ [1+(σ−A)2]e (−Bσ), we investigate the evolutional behavior of Om with respect to red-shift z and the influence of coupling parameter α on the trajectory of Om with respect to z. We get that phantom model of Dilaton dark energy can avoid the future singularity “Big Rip”. The numerical results give current value of EOS which fits the latest observational data WMAP5+BAO+SNe very well. 相似文献
2.
Om diagnostic is a useful geometric method to differentiate between different cosmological models without the accurate current value of matter density. We investigate the Om diagnostic for viscous Cardassian universe and find that the model can be easily distinguished from LCDM. We also investigate the influence of the bulk viscosity coefficient τ on the evolutive behavior of Om with respect to redshift z. According to the value of Om(z=0) for viscous Cardassian models, we obtain the current value of equation of state w k0. 相似文献
3.
K. Karami M. Jamil M. Roos S. Ghaffari A. Abdolmaleki 《Astrophysics and Space Science》2012,340(1):175-184
We study the entropy-corrected version of the new agegraphic dark energy (NADE) model and dark matter in a spatially non-flat Universe and in the framework of Hořava-Lifshitz cosmology. For the two cases containing noninteracting and interacting entropy-corrected NADE (ECNADE) models, we derive the exact differential equation that determines the evolution of the ECNADE density parameter. Also the deceleration parameter is obtained. Furthermore, using a parametrization of the equation of state parameter of the ECNADE model as ω Λ(z)=ω 0+ω 1 z, we obtain both ω 0 and ω 1. We find that in the presence of interaction, the equation of state parameter ω 0 of this model can cross the phantom divide line which is compatible with the observation. 相似文献
4.
Anirudh Pradhan Rekha Jaiswal Kanti Jotania Rajeev Kumar Khare 《Astrophysics and Space Science》2012,337(1):401-413
We present two dark energy (DE) models with an anisotropic fluid in Bianchi type-VI
0 space-time by considering time dependent deceleration parameter (DP). The equation of state (EoS) for dark energy ω is found to be time dependent and its existing range for derived models is in good agreement with the recent observations.
Under the suitable condition, the anisotropic models approach to isotropic scenario. We also find that during the evolution
of the universe, the EoS parameter for DE changes from ω>−1 to ω=−1 in first model whereas from ω>−1 to ω<−1 in second model which is consistent with recent observations. The cosmological constant Λ is found to be a positive decreasing
function of time and it approaches a small positive value at late time (i.e. the present epoch) which is corroborated by results
from recent type Ia supernovae observations. The cosmic jerk parameter in our derived models is also found to be in good agreement
with the recent data of astrophysical observations. The physical and geometric aspects of both the models are also discussed
in detail. 相似文献
5.
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
6.
7.
We consider a self consistent system of Bianchi Type-I cosmology and Binary Mixture of perfect fluid and dark energy. The
perfect fluid is taken to be obeying equations of state p
PF
=γρ
PF
with γ∈[0,1]. The dark energy is considered to be obeying a quintessence-like equation of state where the dark energy obeys equation
of state p
DE
=ωρ
DE
where ω∈[−1,0]. Exact solutions to the corresponding Einstein field equations are obtained. Some special cases are discussed and
studied. Further more power law models and exponential models are investigated. 相似文献
8.
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
9.
In this paper we study the evolution of the dark energy parameter within the scope of a spatially homogeneous and isotropic
FRW universe filled with barotropic fluid and dark energy. The scale factor is considered as a power law function of time
which yields a constant deceleration parameter. We consider the case when the dark energy is minimally coupled to the perfect
fluid as well as direct interaction with it. The cosmic jerk parameter in our derived models is consistent with the recent
data of astrophysical observations. It is concluded that in non-interacting case, all the three open, close and flat universes
cross the phantom region whereas in interacting case only open and flat universes cross the phantom region. We find that during
the evolution of the universe, the equation of state (EoS) for dark energy ω
D
changes from ω
D
>−1 to ω
D
<−1, which is consistent with recent observations. 相似文献
10.
A new dark energy model in anisotropic Bianchi type-III space-time with variable equation of state (EoS) parameter has been
investigated in the present paper. To get the deterministic model, we consider that the expansion θ in the model is proportional to the eigen value s2 2\sigma^{2}_{~2} of the shear tensor sj i\sigma^{j}_{~i}. The EoS parameter ω is found to be time dependent and its existing range for this model is in good agreement with the recent observations of
SNe Ia data (Knop et al. in Astrophys. J. 598:102, 2003) and SNe Ia data with CMBR anisotropy and galaxy clustering statistics (Tegmark et al. in Astrophys. J. 606:702, 2004). It has been suggested that the dark energy that explains the observed accelerating expansion of the universe may arise
due to the contribution to the vacuum energy of the EoS in a time dependent background. Some physical aspects of dark energy
model are also discussed. 相似文献
11.
12.
Antonio Pasqua A. Khodam-Mohammadi Mubasher Jamil R. Myrzakulov 《Astrophysics and Space Science》2012,340(1):199-208
Motivated by the holographic principle, it has been suggested that the dark energy density may be inversely proportional to the area A of the event horizon of the universe. However, such a model would have a causality problem. In this work, we consider the entropy-corrected version of the holographic dark energy model in the non-flat FRW universe and we propose to replace the future event horizon area with the inverse of the Ricci scalar curvature. We obtain the equation of state (EoS) parameter ω Λ, the deceleration parameter q and WD￠\Omega_{D}' in the presence of interaction between Dark Energy (DE) and Dark Matter (DM). Moreover, we reconstruct the potential and the dynamics of the tachyon, K-essence, dilaton and quintessence scalar field models according to the evolutionary behavior of the interacting entropy-corrected holographic dark energy model. 相似文献
13.
We analyse the dark energy problem using observational H(z) data plus the curvature constraint given by WMAP. After a non-parametric
statistical study covering the most probable range of Ω
m0 and H
0 from different combination of data, we investigate the possibility of having the dark energy EoS parameter ω
x
≠−1. In order to keep strict flatness (1% of deviation from Ω=1), our results point out this is the case for 0.20≲Ω
m0≲0.23 and H
0≈67 km/s/Mpc, with ω
x
≈−0.55. However, if we admit a 10% deviation from the flatness condition, ω
x
may have any value in the range [−1.2,−0.5] for 0.20≲Ω
m0≲0.35 and 67≲H
0≲74 km/s/Mpc. 相似文献
14.
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
15.
M. Villata 《Astrophysics and Space Science》2012,339(1):7-12
The unexpected discovery of the accelerated cosmic expansion in 1998 has filled the Universe with the embarrassing presence
of an unidentified “dark energy”, or cosmological constant, devoid of any physical meaning. While this standard cosmology
seems to work well at the global level, improved knowledge of the kinematics and other properties of our extragalactic neighborhood
indicates the need for a better theory. We investigate whether the recently suggested repulsive-gravity scenario can account
for some of the features that are unexplained by the standard model. Through simple dynamical considerations, we find that
the Local Void could host an amount of antimatter (∼5×1015
M
⊙) roughly equivalent to the mass of a typical supercluster, thus restoring the matter-antimatter symmetry. The antigravity
field produced by this “dark repulsor” can explain the anomalous motion of the Local Sheet away from the Local Void, as well
as several other properties of nearby galaxies that seem to require void evacuation and structure formation much faster than
expected from the standard model. At the global cosmological level, gravitational repulsion from antimatter hidden in voids
can provide more than enough potential energy to drive both the cosmic expansion and its acceleration, with no need for an
initial “explosion” and dark energy. Moreover, the discrete distribution of these dark repulsors, in contrast to the uniformly
permeating dark energy, can also explain dark flows and other recently observed excessive inhomogeneities and anisotropies
of the Universe. 相似文献
16.
A model for a solar flare, involving magnetic reconnection transferring flux and current between current-carrying magnetic
loops connecting two pairs of footpoints, is generalized to include conservation of magnetic helicity during reconnection,
as well as conservation of current at all four footpoints. For a set of force-free loops, with the ith loop having flux F
i and current I
i, the self and mutual helicities are proportional to the self and mutual inductances with the constant of proportionality
determined by αi=F
i/μ0
I
i. In a constant-α model, the change in magnetic energy is proportional to the change in helicity, and conservation of helicity
implies conservation of magnetic energy, so that a flare cannot occur. In a quadrupolar model, with α1>α2 initially, α1 increases and α2 decreases when flux and current are transferred from loops 1 and 2 to loops 3 and 4. A model that conserves both current
and helicity is constructed; it depends on the initial αs, and otherwise is somewhat simpler than when helicity is neglected. 相似文献
17.
Applying the parametrization of dark energy density, we can construct directly independent-model potentials. In Born-Infeld
type phantom dark energy model, we consider four special parametrization equation of state parameter. The evolutive behavior
of dark energy density with respect to red-shift z, potentials with respect to φ and z are shown mathematically. Moreover, we investigate the effect of parameter η upon the evolution of the constructed potential with respect to z. These results show that the evolutive behavior of constructed Born-Infeld type dark energy model is quite different from
those of the other models. 相似文献
18.
We investigate the interacting NADE model in non-flat universe. The effects of spatial curvature Ω
k
, interaction coefficient α and the main parameter of NADE, n, on EoS parameter w
d
and deceleration parameter q are studied. We obtain a minimum value for n in both early and present time, in order to that our DE model crosses the phantom divide. Also in a closed universe, changing
the sign of q is strongly dependent on α. It has been shown that the quantities w
d
and q have a different treatment for various spatial curvature. At last, we calculate the statefinder diagnostic and w−w
′ analysis in non flat universe. In non flat universe, the statefinder trajectories are discriminated by both n and α. 相似文献
19.
We study the anomalous flux ratio which is observed in some four-image lens systems, where the source lies close to a fold
caustic. In this case two of the images are close to the critical curve and their flux ratio should be equal to unity, instead
in several cases the observed value differs significantly. The most plausible solution is to invoke the presence of substructures,
as for instance predicted by the Cold Dark Matter scenario, located near the two images. In particular, we analyze the two
fold lens systems PG1115+080 and B1555+375, for which there are not yet satisfactory models which explain the observed anomalous
flux ratios. We add to a smooth lens model, which reproduces well the positions of the images but not the anomalous fluxes,
one or two substructures described as singular isothermal spheres. For PG1115+080 we consider a smooth model with the influence
of the group of galaxies described by a SIS and a substructure with mass ∼105
M
⊙ as well as a smooth model with an external shear and one substructure with mass ∼108
M
⊙. For B1555+375 either a strong external shear or two substructures with mass ∼107
M
⊙ reproduce the data quite well. 相似文献
20.
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