共查询到20条相似文献,搜索用时 46 毫秒
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2.
Piyali Bagchi Khatua Shuvendu Chakraborty Ujjal Debnath 《International Journal of Theoretical Physics》2012,51(2):405-417
In this work, we have considered dilaton dark energy model in Weyl-scaled induced gravitational theory in presence of barotropic
fluid. It is to be noted that the dilaton field behaves as a quintessence. Here we have discussed the role of dilaton dark
energy in modified gravity theories, namely f(R),f(T) and Hořava-Lifshitz gravities and analyzed the behavior of the dilaton field and the corresponding potential in respect
to these modified gravity theories instead of Einstein’s gravity. In f(R) and f(T) gravities, we have considered some particular forms of f(R) and f(T) and we have shown that the potentials always increase with the dilaton fields. But in Hořava-Lifshitz gravity, it has been
seen that the potential always decreases as dilation field increases. 相似文献
3.
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
4.
Hyung Won Lee Kyoung Yee Kim Yun Soo Myung 《The European Physical Journal C - Particles and Fields》2011,71(9):1748
We investigate the issues of future oscillations around the phantom divide (FOPD) for f(R) gravity. For this purpose, we introduce two types of energy density and pressure arisen from the f(R)-higher order curvature terms. One has the conventional energy density and pressure even in the beginning of the Jordan frame,
whose continuity equation defines the native equation of state w
DE. On the other hand, the other has the different energy density and pressure which do not obviously satisfy the continuity
equation. This needs to introduce the effective equation of state w
eff to describe the f(R)-fluid, in addition to the native equation of state [(w)\tilde]DE\tilde{w}_{\mathrm{DE}}. We show that the FOPD occur in f(R) gravities by introducing two types of equation of state. Finally, we point out that the singularity appears ar x=x
c
because the stability condition of f(R) gravity violates. 相似文献
5.
Nairwita Mazumder Subenoy Chakraborty 《International Journal of Theoretical Physics》2011,50(1):251-259
In this paper, we investigate the validity of the generalized second law of thermodynamics of the universe bounded by the
event horizon. Here we consider homogeneous and isotropic model of the universe filled with perfect fluid in one case and
in another case holographic model of the universe has been considered. In the third case the matter in the universe is taken
in the form of non-interacting two fluid system as holographic dark energy and dust. Here we study the above cases in the
Modified gravity, f(R) gravity. 相似文献
6.
We study the effect of modified gravity on weak lensing in a class of scalar-tensor theory that includes f(R) gravity as a special case. These models are designed to satisfy local gravity constraints by having a large scalar-field mass in a region of high curvature. Matter density perturbations in these models are enhanced at small redshifts because of the presence of a coupling Q that characterizes the strength between dark energy and non-relativistic matter. We compute a convergence power spectrum of weak lensing numerically and show that the spectral index and the amplitude of the spectrum in the linear regime can be significantly modified compared to the ΛCDM model for large values of |Q| of the order of unity. Thus weak lensing provides a powerful tool to constrain such large coupling scalar-tensor models including f(R) gravity. 相似文献
7.
In this paper, the metric approach of f(R) theory of gravity is used to investigate the exact vacuum solutions of spatially homogeneous rotating spacetimes. For this purpose, R is replaced by f(R) in the standard Einstein-Hilbert action and the set of modified Einstein field equations reduce to a single equation. We adopt the assumption of constant Ricci scalar which maybe zero or non-zero. Moreover, the energy density of the non-trivial solution has been evaluated by using the generalized Landau-Lifshitz energy-momentum complex in the perspective of f(R) gravity for some appropriate f(R) model, which turns out to be a constant quantity. 相似文献
8.
Hyung Won Lee Kyoung Yee Kim Yun Soo Myung 《The European Physical Journal C - Particles and Fields》2011,71(3):1585
We investigate the Brans–Dicke (BD) theory with the potential as cosmological model to explain the present accelerating universe.
In this work, we consider the BD field as a perfect fluid with the energy density and pressure in the Jordan frame. Introducing
the power-law potential and the interaction with the cold dark matter, we obtain the phantom divide which is confirmed by
the native and effective equation of state. Also we can describe the metric f(R) gravity with an appropriate potential, which shows a future crossing of the phantom divide in viable f(R) gravity models when employing the native and effective equations of state. 相似文献
9.
The well-known energy problem is discussed in f (R) theory of gravity. We use the generalized Landau–Lifshitz energy–momentum complex in the framework of metric f (R) gravity to evaluate the energy density of plane symmetric solutions for some general f (R) models. In particular, this quantity is found for some popular choices of f (R) models. The constant scalar curvature condition and the stability condition for these models are also discussed. Further,
we investigate the energy distribution of cosmic string spacetime. 相似文献
10.
We study a cosmological implication of holographic dark energy in the Brans–Dicke gravity. We employ the holographic model of dark energy to obtain the equation of state for the holographic energy density in non-flat (closed) universe enclosed by the event horizon measured from the sphere of horizon named L. Our analysis shows that one can obtain the phantom crossing scenario if the model parameter α (of order unity) is tuned accordingly. Moreover, this behavior is achieved by treating the Brans–Dicke scalar field as a Chameleon scalar field and taking a non-minimal coupling of the scalar field with matter. Hence one can generate phantom-like equation of state from a holographic dark energy model in non-flat universe in the Brans–Dicke cosmology framework. 相似文献
11.
SUN Cheng-Yi 《理论物理通讯》2011,56(1):193-198
In the paper, we apply the weak gravity conjecture to the holographic quintessence model of dark energy. Three different holographic dark energy models are considered: without the interaction in the non-flat universe; with interaction in the flat universe; with interaction in the non-flat universe. We find that
only in the models with the spatial curvature and interaction term proportional to the energy density of matter, it is possible for the weak gravity conjecture to be satisfied. And it seems that the weak gravity conjecture favors an open universe and the decaying of matter into dark energy. 相似文献
12.
Yue-Yue Zhao Ya-Bo Wu Jian-Bo Lu Zhuo Zhang Wei-Li Han Liang-Liang Lin 《The European Physical Journal C - Particles and Fields》2012,72(3):1924
A modified f(G) gravity model with coupling between matter and geometry is proposed, which is described by the product of the Lagrange density
of the matter and an arbitrary function of the Gauss–Bonnet term. The field equations and the equations of motion corresponding
to this model show the non-conservation of the energy-momentum tensor, the presence of an extra force acting on test particles
and non-geodesic motion. Moreover, the energy conditions and the stability criterion at the de Sitter point in modified f(G) gravity models with curvature–matter coupling are derived, which can degenerate to the well-known energy conditions in general
relativity. Furthermore, in order to get some insight in the meaning of these energy conditions, we apply them to the specific
models of f(G) gravity and the corresponding constraints on the models are given. In addition, the conditions and the candidate for late-time
cosmic accelerated expansion in modified f(G) gravity are studied by means of conditions of power-law expansion and the equation of state of matter ω smaller than
-\frac13-\frac{1}{3}. 相似文献
13.
M. Hamani Daouda Manuel E. Rodrigues M. J. S. Houndjo 《The European Physical Journal C - Particles and Fields》2012,72(2):1893
We develop the reconstruction of the f(T) gravity model according to the holographic dark energy. T is the torsion scalar and its initial value from the teleparallel gravity is imposed for fitting the initial value of the
function f(T). The evolutionary nature of the holographic dark energy is essentially based on two important parameters, Ω
V
and ω
V
, respectively, the dimensionless dark energy and the parameter of the equation of state, related to the holographic dark
energy. The result shows a polynomial function for f(T), and we also observe that, when Ω
V
→1 at the future time, ω
V
may cross −1 for some values of the input parameter b. Another interesting aspect of the obtained model is that it provides a unification scenario of dark matter with dark energy. 相似文献
14.
The purpose of this paper is to discuss the evolution of modified holographic dark energy with variable G in non-flat Kaluza–Klein universe. We consider the non-interacting and interacting scenarios of the modified holographic
dark energy with dark matter and obtain the equation of state parameter through logarithmic approach. It turns out that the
universe remains in different dark energy eras for both cases. Further, we study the validity of the generalized second law
of thermodynamics in this scenario. We also justify that the statefinder parameters satisfy the limit of ΛCDM model. 相似文献
15.
Taeyoon Moon Yun Soo Myung Edwin J. Son 《The European Physical Journal C - Particles and Fields》2011,71(10):1777
We study the stability of the f(R)-AdS (Schwarzschild–AdS) black hole obtained from f(R) gravity. In order to resolve the difficulty of solving fourth-order linearized equations, we transform f(R) gravity into scalar–tensor theory by introducing two auxiliary scalars. In this case, the linearized curvature scalar becomes
a dynamical scalaron, showing that all linearized equations are second order. Using the positivity of gravitational potentials
and S-deformed technique allows us to guarantee the stability of f(R)-AdS black hole if the scalaron mass squared satisfies the Breitenlohner–Freedman bound. This is confirmed by computing quasinormal
frequencies of the scalaron for the f(R)-AdS black hole. 相似文献
16.
A. Aghmohammadi K. Saaidi M. R. Abolhassani A. Vajdi 《International Journal of Theoretical Physics》2010,49(4):709-716
A static, asymptotically flat, spherically symmetric solutions is investigated in f(R) theories of gravity for a charged black hole. We have studied the weak field limit of f(R) gravity for the some f(R) model such as f(R)=R+ε
h(R). In particular, we consider the case lim
R→0
h(R)/h′(R)→0 and find the space time metric for
f(R)=R+[(m4)/(R)]f(R)=R+{\mu^{4}\over R}
and f(R)=R
1+ε
theories of gravity far away a charged mass point. 相似文献
17.
M. F. Shamir 《Journal of Experimental and Theoretical Physics》2016,123(6):979-984
Modified theories of gravity have attracted much attention of the researchers in the recent years. In particular, the f(R) theory has been investigated extensively due to important f(R) gravity models in cosmological contexts. This paper is devoted to exploring an anisotropic universe in metric f(R) gravity. A locally rotationally symmetric Bianchi type I cosmological model is considered for this purpose. Exact solutions of modified field equations are obtained for a well-known f(R) gravity model. The energy conditions are also discussed for the model under consideration. The viability of the model is investigated via graphical analysis using the present-day values of cosmological parameters. The model satisfies null energy, weak energy, and dominant energy conditions for a particular range of the anisotropy parameter while the strong energy condition is violated, which shows that the anisotropic universe in f(R) gravity supports the crucial issue of accelerated expansion of the universe. 相似文献
18.
We investigate propagations of graviton and additional scalar on four-dimensional anti-de Sitter (AdS4) space using f(R) gravity models with external sources. It is shown that there is the van Dam–Veltman–Zakharov (vDVZ) discontinuity in f(R) gravity models because f(R) gravity implies GR with additional scalar. This clearly indicates a difference between general relativity and f(R) gravity. 相似文献
19.
This paper is devoted to studying charged anisotropic static spherically symmetric solutions through gravitationally decoupled minimal geometric deformation technique in f(R) gravity. For this purpose, we first consider the known isotropic Krori–Barua solution for f(R) Starobinsky model in the interior of a charged stellar system and then include the effects of two types of anisotropic solutions. The corresponding field equations are constructed and the unknown constants are obtained from junction conditions. We analyze the physical viability and stability of the resulting solutions through effective energy density, effective radial/tangential pressure, energy conditions, and causality condition. It is found that both solutions satisfy the stability range as well as other physical conditions for specific values of charge as well as model parameter and anisotropic constant. We conclude that the modified theory under the influence of charge yields more stable behavior of the self-gravitating system. 相似文献
20.
Xian Gao 《Physics letters. [Part B]》2011,702(4):197-200
We show that modified gravity presents distinctive nonlinear features on the Cosmic Microwave Background (CMB) anisotropies comparing with General Relativity (GR). We calculate the contribution to the CMB non-Gaussianity from nonlinear Sachs-Wolfe effect in f(R) gravity and show that, contrary to GR?s contribution which is typically ?O(1), the contribution in f(R) gravity is sensitive to the nonlinear structure of f(R) and can be large in principle. Optimistically, this gives an alternative origin for the possibly observed large CMB non-Gaussianities besides the primordial ones. On the other hand, such nonlinear features can be employed to provide a new cosmological test of f(R) or other modified theories of gravitation, which is unique and independent of previously known tests. 相似文献