共查询到20条相似文献,搜索用时 31 毫秒
1.
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
2.
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
3.
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
4.
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
5.
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
6.
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
7.
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
8.
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
9.
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
10.
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
11.
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
12.
Salvatore Capozziello Mariafelicia De Laurentis Luca Fabbri Stefano Vignolo 《The European Physical Journal C - Particles and Fields》2012,72(2):1908
The f(R)-gravitational theory with torsion is considered for one family of leptons; it is found that the torsion tensor gives rise
to interactions having the structure of the weak forces, while the intrinsic non-linearity of the f(R) function provides an energy-dependent coupling: in this way, torsional f(R) gravity naturally generates both structure and strength of the electroweak interactions among leptons. This implies that
the weak interactions among the lepton fields could be addressed as a geometric effect due to the interactions among spinors
induced by the presence of torsion in the most general f(R) gravity. Phenomenological considerations are given. 相似文献
13.
In a recent paper (Sharif and Shamir in Class. Quantum Grav. 26:235020, 2009), we have studied the vacuum solutions of Bianchi
types I and V spacetimes in the framework of metric f (R) gravity. Here we extend this work to perfect fluid solutions. For this purpose, we take stiff matter to find energy density
and pressure of the universe. In particular, we find two exact solutions in each case which correspond to two models of the
universe. The first solution gives a singular model while the second solution provides a non-singular model. The physical
behavior of these models has been discussed using some physical quantities. Also, the function of the Ricci scalar is evaluated. 相似文献
14.
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
15.
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
16.
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
17.
In this paper, we propose two new models in f(T) gravity to realize the crossing of the phantom divide line for the effective equation of state, and we then study the observational
constraints on the model parameters. The best fit results suggest that the observations favor a crossing of the phantom divide
line. 相似文献
18.
Michel Planat 《International Journal of Theoretical Physics》2010,49(5):1044-1054
In quantum information context, the groups generated by Pauli spin matrices, and Dirac gamma matrices, are known as the single
qubit Pauli group ℘, and two-qubit Pauli group ℘2, respectively. It has been found (Socolovsky, Int. J. Theor. Phys. 43: 1941, 2004) that the CPT group of the Dirac equation is isomorphic to ℘. One introduces a two-qubit entangling orthogonal matrix S basically related to the CPT symmetry. With the aid of the two-qubit swap gate, the S matrix allows the generation of the three-qubit real Clifford group and, with the aid of the Toffoli gate, the Weyl group
W(E
8) is generated (Planat, Preprint , 2009). In this paper, one derives three-qubit entangling groups [(P)\tilde]\tilde{\mathcal{P}} and [(P)\tilde]2\tilde{\mathcal{P}}_{2}, isomorphic to the CPT group ℘ and to the Dirac group ℘2, that are embedded into W(E
8). One discovers a new class of pure three-qubit quantum states with no-vanishing concurrence and three-tangle that we name
CPT states. States of the GHZ and CPT families, and also chain-type states, encode the new representation of the Dirac group and its CPT subgroup. 相似文献
19.
This paper contains the study of spherically symmetric perfect fluid collapse in the frame work of f(R, T) modified theory of gravity. We proceed our work by considering the non-static spherically symmetric background in the interior and static spherically symmetric background in the exterior regions of the star. The junction conditions between exterior and interior regions are presented by matching the exterior and interior regions. The field equations are solved by taking the assumptions that the Ricci scalar as well as the trace of energy-momentum tensor are to be constant, for a particular f(R, T) model. By inserting the solution of the field equations in junction conditions, we evaluate the gravitational mass of the collapsing system. Also, we discuss the apparent horizons and their time formation for different possible cases. It is concluded that the term f(R 0, T 0) behaves as a source of repulsive force and that’s why it slowdowns the collapse of the matter. 相似文献
20.
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