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1.
We investigate the QCD ghost model of dark energy in the framework of RS II braneworld. We assume there is an energy flow between the brane and bulk, and hence the continuity equation for the ghost dark energy is violated, while it is still preserved for the dark matter on the brane. We find that with the brane-bulk interaction, the equation of state parameter of ghost dark energy on the brane, can cross the phantom line w D =?1 at the present time, which confirms by some cosmological evidences. This result is in contrast to the standard cosmology where w D of ghost dark energy never cross the phantom line and the universe enters a de Sitter phase at the late time. 相似文献
2.
Esmaeil Ebrahimi Ahmad Sheykhi Hamzeh Alavirad 《Central European Journal of Physics》2013,11(7):949-960
We investigate the generalized Quantum Chromodynamics (QCD) ghost model of dark energy in the framework of Einstein gravity. First, we study the non-interacting generalized ghost dark energy in a flat Friedmann-Robertson-Walker (FRW) background. We obtain the equation of state parameter, w D = p/ρ, the deceleration parameter, and the evolution equation of the generalized ghost dark energy. We find that, in this case, w D cannot cross the phantom line (w D > ?1) and eventually the universe approaches a de-Sitter phase of expansion (w D → ?1). Then, we extend the study to the interacting ghost dark energy in both a flat and non-flat FRW universe. We find that the equation of state parameter of the interacting generalized ghost dark energy can cross the phantom line (w D < ?1) provided the parameters of the model are chosen suitably. Finally, we constrain the model parameters by using the Markov Chain Monte Carlo (MCMC) method and a combined dataset of SNIa, CMB, BAO and X-ray gas mass fraction. 相似文献
3.
In this paper we put forward a running coupling scenario for describing the interaction between dark energy and dark matter.
The dark sector interaction in our scenario is free of the assumption that the interaction term Q is proportional to the Hubble expansion rate and the energy densities of dark sectors. We only use a time-variable coupling
b(a) (with a the scale factor of the universe) to characterize the interaction Q. We propose a parametrization form for the running coupling b(a)=b
0
a+b
e
(1−a) in which the early-time coupling is given by a constant b
e
, while today the coupling is given by another constant, b
0. For investigating the feature of the running coupling, we employ three dark energy models, namely, the cosmological constant
model (w=−1), the constant w model (w=w
0), and the time-dependent w model (w(a)=w
0+w
1(1−a)). We constrain the models with the current observational data, including the type Ia supernova, the baryon acoustic oscillation,
the cosmic microwave background, the Hubble expansion rate, and the X-ray gas mass fraction data. The fitting results indicate
that a time-varying vacuum scenario is favored, in which the coupling b(z) crosses the noninteracting line (b=0) during the cosmological evolution and the sign changes from negative to positive. The crossing of the noninteracting line
happens at around z=0.2–0.3, and the crossing behavior is favored at about 1σ confidence level. Our work implies that we should pay more attention to the time-varying vacuum model and seriously consider
the phenomenological construction of a sign-changeable or oscillatory interaction between dark sectors. 相似文献
4.
A. Sheykhi K. Karami M. Jamil E. Kazemi M. Haddad 《General Relativity and Gravitation》2012,44(3):623-638
In the derivation of holographic dark energy density, the area law of the black hole entropy plays a crucial role. However,
the entropy-area relation can be modified from the inclusion of quantum effects, motivated from the loop quantum gravity,
string theory and black hole physics. In this paper, we study cosmological implication of the interacting entropy-corrected
holographic dark energy model in the framework of Brans–Dicke cosmology. We obtain the equation of state and the deceleration
parameters of the entropy-corrected holographic dark energy in a non-flat Universe. As system’s IR cutoff we choose the radius
of the event horizon measured on the sphere of the horizon, defined as L = ar(t). We find out that when the entropy-corrected holographic dark energy is combined with the Brans–Dicke field, the transition
from normal state where w
D
> −1 to the phantom regime where w
D
< −1 for the equation of state of interacting dark energy can be more easily achieved for than when resort to the Einstein
field equations is made. 相似文献
5.
A new dark energy model called “ghost dark energy” was recently suggested to explain the observed accelerating expansion of the universe. This model originates from the Veneziano ghost of QCD. The dark energy density is proportional to Hubble parameter, ρ Λ = α H, where α is a constant of order \({\Lambda }^{3}_{QCD}\) and Λ Q C D ~ 100M e V is QCD mass scale. In this paper, we investigate about the stability of generalized QCD ghost dark energy model against perturbations in the anisotropic background. At first, the ghost dark energy model of the universe with spatial BI model with/without the interaction between dark matter and dark energy is discussed. In particular, the equation of state and the deceleration parameters and a differential equation governing the evolution of this dark energy model are obtained. Then, we use the squared sound speed \({v_{s}^{2}}\) the sign of which determines the stability of the model. We explore the stability of this model in the presence/absence of interaction between dark energy and dark matter in both flat and non-isotropic geometry. In conclusion, we find evidence that the ghost dark energy might can not lead to a stable universe favored by observations at the present time in BI universe. 相似文献
6.
Mubasher Jamil K. Karami A. Sheykhi E. Kazemi Z. Azarmi 《International Journal of Theoretical Physics》2012,51(2):604-611
Motivated by the recent works of one of us (Karami and Fehri, Int. J. Theor. Phys. 49:1118, 2010; Phys. Lett. B 684:61, 2010), we study the holographic dark energy in Brans-Dicke gravity with the Granda-Oliveros cut-off proposed recently in literature.
We find out that when the present model is combined with Brans-Dicke field the transition from normal state where w
D
>−1 to the phantom regime where w
D
<−1 for the equation of state of dark energy can be more easily achieved for than when resort to the Einstein field equations
is made. Furthermore, the phantom crossing is more easily achieved when the matter and the holographic dark energy undergo
an exotic interaction. We also calculate some relevant cosmological parameters and their evolution. 相似文献
7.
M. Malekjani A. Khodam-Mohammadi 《International Journal of Theoretical Physics》2012,51(10):3141-3151
The interacting polytropic gas dark energy model is investigated from the viewpoint of statefinder diagnostic tool and w−w′ analysis. The dependency of the statefinder parameters on the parameter of the model as well as the interaction parameter between dark matter and dark energy is calculated. We show that different values of the parameters of model and different values of interaction parameter result different evolutionary trajectories in s−r and w−w′ planes. The polytropic gas model of dark energy mimics the standard ΛCDM model at the early time. 相似文献
8.
A. Sheykhi K. Karami M. Jamil E. Kazemi M. Haddad 《International Journal of Theoretical Physics》2012,51(6):1663-1673
Considering the power-law corrections to the black hole entropy, which appear in dealing with the entanglement of quantum
fields inside and outside the horizon, the holographic energy density is modified accordingly. In this paper we study the
power-law entropy-corrected holographic dark energy in the framework of Brans-Dicke theory. We investigate the cosmological
implications of this model in detail. We also perform the study for the new agegraphic dark energy model and calculate some
relevant cosmological parameters and their evolution. As a result we find that this model can provide the present cosmic acceleration
and even the equation of state parameter of this model can cross the phantom line w
D
=−1 provided the model parameters are chosen suitably. 相似文献
9.
Hassan Amirhashchi Anirudh Pradhan H. Zainuddin 《International Journal of Theoretical Physics》2011,50(11):3529-3543
We study the evolution of the dark energy parameter in a spatially homogeneous and isotropic FRW space-time filled with barotropic
fluid and dark energy by considering a time dependent deceleration parameter. Two cases are discussed when the dark energy
is minimally coupled to the perfect fluid as well as direct interaction with it. It is concluded that in both non-interacting
and interacting cases 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. The cosmic jerk parameter in our derived models is also found to be in
good agreement with the recent data of astrophysical observations. 相似文献
10.
Jianbo Lu Lixin Xu Molin Liu Yuanxing Gui 《The European Physical Journal C - Particles and Fields》2008,58(2):311-324
We use recent data: the 192 ESSENCE type Ia supernovae (SNe Ia), the 182 Gold SNe Ia, the three-year WMAP, the SDSS baryon
acoustic peak, the X-ray gas mass fraction in clusters and the observational H(z) data, to constrain models of the accelerating universe. Combining the 192 ESSENCE data with the observational H(z) data to constrain the parameterized deceleration parameter, we obtain the best-fit values of the transition redshift and
current deceleration parameter z
T=0.632−0.127+0.256 and q
0=−0.788−0.182+0.182. Furthermore, using the ΛCDM model and two model-independent equations of state of the dark energy, we find that the combined
constraint from the 192 ESSENCE data and four other cosmological observations gives smaller values for Ω
0m and q
0, but a larger value for z
T than the combined constraint from the 182 Gold data with four other observations. Finally, according to the Akaike information
criterion it is shown that the recently observed data equally support three dark energy models: ΛCDM, w
de(z)=w
0 and w
de(z)=w
0+w
1ln (1+z). 相似文献
11.
We investigate the QCD ghost model of dark energy in the framework of Brans-Dicke cosmology. First, we study the non-interacting ghost dark energy in a flat Brans-Dicke theory. In this case we obtain the equation of state and the deceleration parameters and a differential equation governing the evolution of ghost energy density. Interestingly enough, we find that the equation of state parameter of the non-interacting ghost dark energy can cross the phantom line (wD=−1) provided the parameters of the model are chosen suitably. Then, we generalize the study to the interacting ghost dark energy in both flat and non-flat Brans-Dicke framework and find out that the transition of wD to phantom regime can be more easily achieved for than when resort to the Einstein field equations is made. 相似文献
12.
Rong-Jia Yang Jing-Zhao Qi Lihua Feng 《International Journal of Theoretical Physics》2012,51(6):1692-1697
Assuming that the equation of state of dark energy is a constant, we obtain the allowed interval of the equation of state
of dark energy: w
D≥−1, bounded from the generalized second law of thermodynamics, in a universe enveloped by the apparent horizon and containing
a Schwarzschild black hole. 相似文献
13.
In this work, the generalized Quantum Chromodynamics (QCD) ghost model of dark energy in the framework of Einstein gravity is investigated. At first, the non-interacting generalized ghost dark energy in a Bianchi type I (BI) background is discussed. Then the equation of state parameter, ω D = p D /ρ D , the deceleration parameter, and the evolution equation of the generalized ghost dark energy are obtained. It was found that, in this case, ω D cannot cross the phantom line (ω D >?1) and eventually the universe approaches a de-Sitter phase of expansion (ω D →?1). Then, this investigation was extended to the interacting ghost dark energy in a non-isotropic universe. It was found that the equation of state parameter of the interacting generalized ghost dark energy can cross the phantom line (ω D <?1) provided the parameters of the model are chosen suitably. It was considered a specific model which permits the standard continuity equation in this theory. Besides ΩΛ and Ω m in standard Einstein cosmology, another density parameter, Ω σ , is expected by the anisotropy. The anisotropy of the universe decreases and the universe transits to an isotropic flat FRW universe accommodating the present acceleration. 相似文献
14.
Recent observations of the Cosmic Microwave Background, Supernovae and Sloan Digital Sky Survey (SDSS) show that our universe has a critical energy density, and roughly 2/3 of it is dark energy, which drives the accelerating expansion of the cosmos. In view of the astrophysical data, we find that the equation of state parameter of the dark energy lies in a narrow range around w = −1. In this paper, we construct a cosmology model with a Rarita-Schwinger field to realize the equation of state parameter w < −1 or w > −1 and discuss its stability. 相似文献
15.
Abhik Kumar Sanyal 《General Relativity and Gravitation》2009,41(7):1511-1525
Smooth double crossing of the phantom barrier w
Λ = − 1 has been found possible in cosmological model with Gauss–Bonnet-scalar interaction, in the presence of background cold
dark matter. Such crossing has been observed to be a sufficiently late time phenomena and independent of the sign of Gauss–Bonnet-scalar
interaction. The luminosity distance versus redshift curve shows a perfect fit with the Λ CDM model up to z = 3.5. 相似文献
16.
We analyze an oscillating universe model in brane world cenario. The oscillating universe cycles through a series of expansions
and contractions and its energy density is dominated by dust matter at early-time expansion phase and by phantom dark energy
at late-time expansion phase. We find that the period of the oscillating universe is not sensitive to the tension of the brane,
but sensitive to the equation-of-state parameter w of the phantom dark energy, and the ratio of the period to the current Hubble age approximately varies from 3 to 9 when the
parameter w changes from −1.4 to −1.1. The fraction of time that the oscillating universe spends in the coincidence state is also comparable
to the period of the oscillating universe. This result indicates that the coincidence problem can be significantly ameliorated
in the oscillating universe without singularity. 相似文献
17.
In this work we consider the entropy-corrected version of interacting holographic dark energy (HDE), in the non-flat universe
enclosed by apparent horizon. Two corrections of entropy so-called logarithmic ‘LEC’ and power-law ‘PLEC’ in HDE model with
apparent horizon as an IR-cutoff are studied. The ratio of dark matter to dark energy densities u, equation of state parameter w
D
and deceleration parameter q are obtained. We show that the cosmic coincidence problem is solved for interacting models. By studying the effect of interaction
in EoS parameter of both models, we see that the phantom divide may be crossed and also understand that the interacting models
can drive an acceleration expansion at the present and future, while in non-interacting case, this expansion can happen only
at the early time. The graphs of deceleration parameter for interacting models, show that the present acceleration expansion
is preceded by a sufficiently long period deceleration at past. Moreover, the thermodynamical interpretation of interaction
between LECHDE and dark matter is described. We obtain a relation between the interaction term of dark components and thermal
fluctuation in a non-flat universe, bounded by the apparent horizon. In limiting case, for ordinary HDE, the relation of interaction
term versus thermal fluctuation is also calculated. 相似文献
18.
Recent observations on Type-Ia supernovae and low density (Ω
m
=0.3) measurement of matter including dark matter suggest that the present-day universe consists mainly of repulsive-gravity
type ‘exotic matter’ with negative-pressure often said ‘dark energy’ (Ω
x
=0.7). But the nature of dark energy is mysterious and its puzzling questions, such as why, how, where and when about the
dark energy, are intriguing. In the present paper the authors attempt to answer these questions while making an effort to
reveal the genesis of dark energy and suggest that ‘the cosmological nuclear binding energy liberated during primordial nucleo-synthesis
remains trapped for a long time and then is released free which manifests itself as dark energy in the universe’. It is also
explained why for dark energy the parameter
w=-\frac23w=-\frac{2}{3}
. Noting that w=1 for stiff matter and
w=\frac13w=\frac{1}{3}
for radiation;
w=-\frac23w=-\frac{2}{3}
is for dark energy because “−1” is due to ‘deficiency of stiff-nuclear-matter’ and that this binding energy is ultimately
released as ‘radiation’ contributing “
+\frac13+\frac{1}{3}
”, making
w=-1+\frac13=-\frac23w=-1+\frac{1}{3}=-\frac{2}{3}
. When dark energy is released free at Z=80,
w=-\frac23w=-\frac{2}{3}
. But as on present day at Z=0 when the radiation-strength-fraction (δ), has diminished to δ→0, the
w=-1+d\frac13=-1w=-1+\delta\frac{1}{3}=-1
. This, almost solves the dark-energy mystery of negative pressure and repulsive-gravity. The proposed theory makes several
estimates/predictions which agree reasonably well with the astrophysical constraints and observations. Though there are many
candidate-theories, the proposed model of this paper presents an entirely new approach (cosmological nuclear energy) as a
possible candidate for dark energy. 相似文献
19.
20.
Jianbo Lu Yuanxing Gui Li xin Xu 《The European Physical Journal C - Particles and Fields》2009,63(3):349-354
We investigate observational constraints on the generalized Chaplygin gas (GCG) model as the unification of dark matter and
dark energy from the latest observational data: the Union SNe Ia data, the observational Hubble data, the SDSS baryon acoustic
peak and the five-year WMAP shift parameter. The result is obtained that the best-fit values of the GCG model parameters with
their confidence level are A
s=0.73−0.06+0.06 (1σ) −0.09+0.09 (2σ), α=−0.09−0.12+0.15 (1σ) −0.19+0.26 (2σ). Furthermore, in this model, we can see that the evolution of equation of state (EOS) for dark energy is similar to quiessence,
and its current best-fit value is w
0de=−0.96 with the 1σ confidence level −0.91≥w
0de≥−1.00. 相似文献