共查询到20条相似文献,搜索用时 15 毫秒
1.
Recently f(T) theories based on modifications of teleparallel gravity, where torsion is the geometric object describing gravity instead
of curvature, have been proposed to explain the present cosmic accelerating expansion. The field equations are always second
order, remarkably simpler than f(R) theories. In analogy to the f(R) theory, we consider here three types of f(T) gravity, and find that all of them can give rise to cosmic acceleration with interesting features, respectively. 相似文献
2.
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
3.
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
4.
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
5.
M. F. Shamir 《Journal of Experimental and Theoretical Physics》2016,122(2):331-337
The modified theories of gravity, especially the f(R) gravity, have attracted much attention in the last decade. This paper is devoted to exploring plane-symmetric solutions in the context of metric f(R) gravity. We extend the work on static plane-symmetric vacuum solutions in f(R) gravity already available in the literature [1, 2]. The modified field equations are solved using the assumptions of both constant and nonconstant scalar curvature. Some well-known solutions are recovered with power-law and logarithmic forms of f(R) models. 相似文献
6.
In this paper, we reconstruct cosmological models in the framework of f(R,T) gravity, where R is the Ricci scalar and T is the trace of the stress-energy tensor. We show that the dust fluid reproduces ΛCDM, phantom–non-phantom era and phantom cosmology. Further, we reconstruct different cosmological models, including the Chaplygin
gas, and scalar field with some specific forms of f(R,T). Our numerical simulation for the Hubble parameter shows good agreement with the BAO observational data for low redshifts,
z<2. 相似文献
7.
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
8.
From a macroscopic theory of the quantum vacuum in terms of conserved relativistic charges (generically denoted by q
(a) with label a), we have obtained, in the low-energy limit, a particular type of f(R) model relevant to cosmology. The macroscopic quantum-vacuum theory allows us to distinguish between different phenomenological
f(R) models on physical grounds.
The text was submitted by the authors in English. 相似文献
9.
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
10.
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
11.
In this paper we study the Geodesic Deviation Equation (GDE) in metric f (R) gravity. We start giving a brief introduction of the GDE in General Relativity in the case of the standard cosmology. Next
we generalize the GDE for metric f (R) gravity using again the FLRW metric. A generalization of the Mattig relation is also obtained. Finally we give and equivalent
expression to the Dyer-Roeder equation in General Relativity in the context of f (R) gravity. 相似文献
12.
M. Hamani Daouda Manuel E. Rodrigues M. J. S. Houndjo 《The European Physical Journal C - Particles and Fields》2011,71(11):1817
We consider the equations of motion of an anisotropic space-time in f(T) theory, where T is the torsion. New spherically symmetric solutions of black holes and wormholes are obtained with a constant torsion and
for the cases for which the radial pressure is proportional to a real constant, to some algebraic functions f(T) and their derivatives f
T
(T), or vanishes identically. 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):1890
In previous work, we undertook to study static and anisotropic content in f(T) theory and obtained new spherically symmetric solutions considering a constant torsion and some particular conditions for
the pressure. In this paper, still in the framework of f(T) theory, new spherically symmetric solutions are obtained, first considering the general case of an isotropic fluid and later
the anisotropic content case in which the generalized conditions for the matter content are considered such that the energy
density, the radial and tangential pressures depend on the algebraic f(T) and its derivative f
T
(T). Moreover, we obtain the algebraic function f(T) through the reconstruction method for two cases and also study a polytropic model for the stellar structure. 相似文献
14.
Subhra Bhattacharya Subenoy Chakraborty 《The European Physical Journal C - Particles and Fields》2017,77(8):558
The scalar–tensor f(R) theory of gravity is considered in the framework of a simple inhomogeneous space-time model. In this research we use the reconstruction technique to look for possible evolving wormhole solutions within viable f(R) gravity formalism. These f(R) models are then constrained so that they are consistent with existing experimental data. Energy conditions related to the matter threading the wormhole are analyzed graphically and are in general found to obey the null energy conditions (NEC) in regions around the throat, while in the limit \(f(R)=R,\) NEC can be violated at large in regions around the throat. 相似文献
15.
S. Capozziello M. De Laurentis S. Nojiri S. D. Odintsov 《General Relativity and Gravitation》2009,41(10):2313-2344
We analyze seven different viable f (R)-gravities towards the Solar System tests and stochastic gravitational waves background. The aim is to achieve experimental
bounds for the theory at local and cosmological scales in order to select models capable of addressing the accelerating cosmological
expansion without cosmological constant but evading the weak field constraints. Beside large scale structure and galactic
dynamics, these bounds can be considered complimentary in order to select self-consistent theories of gravity working at the
infrared limit. It is demonstrated that seven viable f (R)-gravities under consideration not only satisfy the local tests, but additionally, pass the above PPN-and stochastic gravitational
waves bounds for large classes of parameters. 相似文献
16.
Crislane S. Santos Janilo Santos Salvatore Capozziello 《General Relativity and Gravitation》2017,49(4):50
The Raychaudhuri equation enables to examine the whole spacetime structure without specific solutions of Einstein’s equations, playing a central role for the understanding of the gravitational interaction in cosmology. In General Relativity, without considering a cosmological constant, a non-positive contribution in the Raychaudhuri equation is usually interpreted as the manifestation of the attractive character of gravity. In this case, particular energy conditions—indeed the strong energy condition—must be assumed in order to guarantee the attractive character. In the context of f(R) gravity, however, even assuming the standard energy conditions one may have a positive contribution to the Raychaudhuri equation. Besides providing a simple way to explain the observed cosmic acceleration, this fact opens the possibility of a repulsive character of this kind of gravity. In order to discuss physical bounds on f(R) models, we address the attractive/non-attractive character of f(R) gravity considering the Raychaudhuri equation and assuming the strong energy condition along with recent estimates of the cosmographic parameters. 相似文献
17.
The recent LIGO observation sparked interest in the field of gravitational wave signals. Besides the gravitational wave observation the LIGO collaboration used the inspiraling black hole pair to constrain the graviton mass. Unlike general relativity, f(R) theories have a characteristic non-zero mass graviton. We apply this constraint on the graviton mass to viable f(R) models in order to find the effects on model parameters. We find it possible to constrain the parameter space with these gravity wave based observations. We consider the popular Hu–Sawicki model as a case study and find an appropriate parameter bracket. The result generalizes to other f(R) theories and can be used to constrain the parameter space. 相似文献
18.
Salvatore Capozziello Arturo Stabile Antonio Troisi 《International Journal of Theoretical Physics》2010,49(6):1251-1261
We formally discuss the post-Minkowskian limit of f(R)-gravity without adopting conformal transformations but developing all the calculations in the original Jordan frame. It
is shown that such an approach gives rise, in general, together with the standard massless graviton, to massive scalar modes
whose masses are directly related to the analytic parameters of the theory. In this sense, the presence of massless gravitons
only is a peculiar feature of General Relativity. This fact is never stressed enough and could have dramatic consequences
in detection of gravitational waves. Finally the role of curvature stress-energy tensor of f(R)-gravity is discussed showing that it generalizes the so called Landau-Lifshitz tensor of General Relativity. The further
degrees of freedom, giving rise to the massive modes, are directly related to the structure of such a tensor. 相似文献
19.
M. Lubini C. Tortora J. Näf Ph. Jetzer S. Capozziello 《The European Physical Journal C - Particles and Fields》2011,71(12):1834
For a general class of analytic f(R)-gravity theories, we discuss the weak field limit in view of gravitational lensing. Though an additional Yukawa term in
the gravitational potential modifies dynamics with respect to the standard Newtonian limit of General Relativity, the motion
of massless particles results unaffected thanks to suitable cancellations in the post-Newtonian limit. Thus, all the lensing
observables are equal to the ones known from General Relativity. Since f(R)-gravity is claimed, among other things, to be a possible solution to overcome for the need of dark matter in virialized
systems, we discuss the impact of our results on the dynamical and gravitational lensing analyses. In this framework, dynamics
could, in principle, be able to reproduce the astrophysical observations without recurring to dark matter, but in the case
of gravitational lensing we find that dark matter is an unavoidable ingredient. Another important implication is that gravitational
lensing, in the post-Newtonian limit, is not able to constrain these extended theories, since their predictions do not differ
from General Relativity. 相似文献
20.
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