共查询到20条相似文献,搜索用时 109 毫秒
1.
Recently, energy condition inequalities in the context of modified Gauss-Bonnet gravity have been derived in Garcia et al. (Phys. Rev. D, 83:104032, 2011). Using these general inequalities, we examine the viability of specific forms of f(G) models proposed in De Felice and Tsujikawa (Phys. Lett. B, 675:1, 2009) that can be responsible for the late-time cosmic acceleration following the matter era. In doing so we also use the recent estimated values of the deceleration, jerk and snap parameters to obtain the bounds from the weak and strong energy conditions on the parameters of the above mentioned forms of f(G) gravity theories. 相似文献
2.
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
3.
Han Dong Ying-bin Wang Xin-he Meng 《The European Physical Journal C - Particles and Fields》2012,72(5):2002
f(T) theory, a generally modified teleparallel gravity, has been proposed as an alternative gravity model to account for the
dark energy phenomena. Following our previous work [Xin-he Meng and Ying-bin Wang, Eur. Phys. J. (2011), ], we prove that Birkhoff’s theorem holds in a more general context, specifically with the off diagonal tetrad case, in this
communication letter. Then, we discuss, respectively, the results of the external vacuum and internal gravitational field
in the f(T) gravity framework, as well as the extended meaning of this theorem. We also investigate the validity of Birkhoff’s theorem
in the frame of f(T) gravity via a conformal transformation by regarding the Brans–Dicke-like scalar as effective matter, and study the equivalence
between both Einstein frame and Jordan frame. 相似文献
4.
Inflationary models of the early universe provide a natural mechanism for the formation of large scale structure. This success
brings to forefront the question of naturalness: Does a sufficiently long slow roll inflation occur generically or does it
require a careful fine tuning of initial parameters? In recent years there has been considerable controversy on this issue
(Hollands and Wald in Gen Relativ Gravit, 34:2043, 2002; Kofman et al. in J High Energy Phys 10:057, 2002); (Gibbons and Turok in Phys Rev D 77:063516, 2008). In particular, for a quadratic potential, Kofman et al. (J High Energy Phys 10:057, 2002) have argued that the probability of inflation with at least 65 e-foldings is close to one, while Gibbons and Turok (Phys
Rev D 77:063516, 2008) have argued that this probability is suppressed by a factor of ~10−85. We first clarify that such dramatically different predictions can arise because the required measure on the space of solutions
is intrinsically ambiguous in general relativity. We then show that this ambiguity can be naturally resolved in loop quantum
cosmology (LQC) because the big bang is replaced by a big bounce and the bounce surface can be used to introduce the structure
necessary to specify a satisfactory measure. The second goal of the paper is to present a detailed analysis of the inflationary
dynamics of LQC using analytical and numerical methods. By combining this information with the measure on the space of solutions,
we address a sharper question than those investigated in Kofman et al. (J High Energy Phys 10:057, 2002), Gibbons and Turok (Phys Rev D 77:063516, 2008), Ashtekar and Sloan (Phys Lett B 694:108, 2010): What is the probability of a sufficiently long slow roll inflation which is compatible with the seven year WMAP data? We show that the probability is very close to 1. The material is so organized that cosmologists who may be more interested
in the inflationary dynamics in LQC than in the subtleties associated with measures can skip that material without loss of
continuity. 相似文献
5.
Motivated by recent work of Sheykhi (Phys. Lett. B 682:329, 2010), we generalize this work to agegraphic tachyon models of dark energy with entropy correction terms arising from loop quantum
gravity. We establish a connection between the entropy-corrected agegraphic dark energy and the tachyon scalar field in a
universe with spacial curvature and reconstruct the potential and the dynamics of the tachyon scalar field which describe
the tachyon cosmology. The cosmological implications of the entropy-corrected agegraphic dark energy models are also discussed. 相似文献
6.
Mubasher Jamil K. Karami A. Sheykhi 《International Journal of Theoretical Physics》2011,50(10):3069-3077
Motivated by recent works (Saridakis in Phys. Lett. B 660:138, 2008; Sheykhi in Int. J. Mod. Phys. D 19(3):305, 2010), we investigate the new agegraphic model of dark energy in the framework of RS II braneworld. We also include the case of
variable gravitational constant G in our model. Moreover, we reconstruct the potential and the dynamics of the quintessence, tachyon, K-essence and dilaton
scalar field models according to the evolutionary behavior of the new agegraphic dark energy model in RS II braneworld cosmology
including varying G. 相似文献
7.
The metric-affine gravity provides a useful framework for analyzing gravitational dynamics since it treats metric tensor and affine connection as fundamentally independent variables. In this work, we show that, a metric-affine gravity theory composed of the invariants formed from non-metricity, torsion and curvature tensors can be decomposed into a theory of scalar, vector and tensor fields. These fields are natural candidates for the ones needed by various cosmological and other phenomena. Indeed, we show that the model accommodates TeVeS gravity (relativistic modified gravity theory), vector inflation, and aether-like models. Detailed analyses of these and other phenomena can lead to a standard metric-affine gravity model encoding scalars, vectors and tensors. 相似文献
8.
S. D. Katore K. S. Adhav A. Y. Shaikh N. K. Sarkate 《International Journal of Theoretical Physics》2010,49(10):2358-2363
An exact higher dimensional LRS Bianchi type-I cosmological model is obtained in presence of thick domain walls in a scalar
tensor theory of gravitation proposed by Saez and Ballester (Phys. Lett. A113:467, 1985). Some physical and kinematical properties of the models are also discussed. 相似文献
9.
The standard cosmology is based on general relativity (GR) and includes dark matter and dark energy and predicts a fixed relationship between the gravitational potentials responsible for gravitational lensing and the matter overdensity. Alternative theories of gravity often make different predictions. We propose a set of measurements which can test this relationship, thereby distinguishing between dark energy or matter models and models in which gravity differs from GR. Planned surveys will be able to measure E(G), an observational quantity whose expectation value is equal to the ratio of the Laplacian of the Newtonian potentials to the peculiar velocity divergence, to percent accuracy. This will easily separate alternatives such as the cold dark matter model with a cosmological constant, Dvali-Gabadadze-Porrati, TeVeS, and f(R) gravity. 相似文献
10.
We report on some implications of the theory of turbulence developed by V. Yakhot (Phys. Rev. E 57(2):1737, 1998). In particular we focus on the expression for the scaling exponents ζ
n
. We show that Yakhot’s result contains three well known scaling models as special cases, namely K41, K62 and the theory by
V. L’vov and I. Procaccia (Phys. Rev. E 62(6):8037, 2000). The model furthermore yields a theoretical justification for the method of extended self-similarity (ESS). 相似文献
11.
All evolutional paths for all admissible initial conditions of FRW cosmological models with dissipative dust fluid (described by dark matter, baryonic matter and dark energy) are analyzed using dynamical system approach. With that approach, one is able to see how generic the class of solutions leading to the desired property—acceleration—is. The theory of dynamical systems also offers a possibility of investigating all possible solutions and their stability with tools of Newtonian mechanics of a particle moving in a one-dimensional potential which is parameterized by the cosmological scale factor. We demonstrate that flat cosmology with bulk viscosity can be treated as a conservative system with a potential function of the Chaplygin gas type. We characterize the class of dark energy models that admit late time de Sitter attractor solution in terms of the potential function of corresponding conservative system. We argue that inclusion of dissipation effects makes the model more realistic because of its structural stability. We also confront viscous models with SNIa observations. The best fitted models are obtained by minimizing the χ2 function which is illustrated by residuals and χ2 levels in the space of model independent parameters. The general conclusion is that SNIa data supports the viscous model without the cosmological constant. The obtained values of χ2 statistic are comparable for both the viscous model and ΛCDM model. The Bayesian information criteria are used to compare the models with different power-law parameterization of viscous effects. Our result of this analysis shows that SNIa data supports viscous cosmology more than the ΛCDM model if the coefficient in viscosity parameterization is fixed. The Bayes factor is also used to obtain the posterior probability of the model. 相似文献
12.
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
13.
K. Daley 《International Journal of Theoretical Physics》2009,48(8):2379-2383
A re-visitation of QFT is first cited, deriving the Feynman integral from the theory of active stochastic processes (Glueck
and Hueffler, Phys. Lett. B. 659(1–2):447–451, 2008; Hueffel and Kelnhofer, Phys. Lett. B 588(1–2):145–150, 2004). We factor the lie group “generator” of the inverse wavefunction over an entropy-maximizing basis. Performing term-by-term
Ito-integration leads us to an analytical, evaluable trajectory for a charged particle in an arbitrary field given a Maximum-Entropy
distribution.
We generalize this formula to many-body electrodynamics. In theory, it is capable of predicting plasma’s thermodynamic properties
from ionic spectral data and thermodynamic and optical distributions. Blessed with the absence of certain limitations (e.g.,
renormalization) strongly present in competing formalisms and the incorporation of research related to many different phenomena,
we outline a candidate quantum gravity theory based on these developments. 相似文献
14.
We give a new proof of universality properties in the bulk of spectrum of the hermitian matrix models, assuming that the potential
that determines the model is globally C
2 and locally C
3 function (see Theorem 3.1). The proof as our previous proof in (Pastur and Shcherbina in J. Stat. Phys. 86:109–147, 1997) is based on the orthogonal polynomial techniques but does not use asymptotics of orthogonal polynomials. Rather, we obtain
the sin -kernel as a unique solution of a certain non-linear integro-differential equation that follows from the determinant
formulas for the correlation functions of the model. We also give a simplified and strengthened version of paper (Boutet de
Monvel, et al. in J. Stat. Phys. 79:585–611, 1995) on the existence and properties of the limiting Normalized Counting Measure of eigenvalues. We use these results in the
proof of universality and we believe that they are of independent interest. 相似文献
15.
Motivated by a recent use of Glauber dynamics for Monte Carlo simulations of path integral representation of quantum spin
models (Krzakala et al. in Phys. Rev. B 78(13):134428, 2008), we analyse a natural Glauber dynamics for the quantum Ising model with a transverse field on a finite graph G. We establish strict monotonicity properties of the equilibrium distribution and we extend (and improve) the censoring inequality
of Peres and Winkler to the quantum setting. Then we consider the case when G is a regular b-ary tree and prove the same fast mixing results established in Martinelli et al. (Commun. Math. Phys. 250(2):301–334, 2004) for the classical Ising model. Our main tool is an inductive relation between conditional marginals (known as the “cavity
equation”) together with sharp bounds on the operator norm of the derivative at the stable fixed point. It is here that the
main difference between the quantum and the classical case appear, as the cavity equation is formulated here in an infinite
dimensional vector space, whereas in the classical case marginals belong to a one-dimensional space. 相似文献
16.
Gülçin Uluyazı 《General Relativity and Gravitation》2012,44(4):875-886
We investigate the relation between the brane-based and the bulk-based approaches for anisotropic case in brane-world models.
In the brane-based approach, the brane is chosen to be fixed on a coordinate system, whereas in the bulk-based approach it
is no longer static as it moves along the extra dimension. It was shown that these two approaches are equivalent for specific
models in Mukohyama et al. (Phys Rev D 62:024028, 2000), Bowcock et al. (Class Quant Gravit 17:4745–4764, 2000). In this paper, it is aimed to get general formalism of the equivalence obtained in Mukohyama et al. (Phys Rev D 62:024028,
2000). We found that calculations driven by a general anisotropic bulk-based metric yield a brane-based metric in Gaussian Normal
Coordinates by conserving spatial anisotropy. We also derive solutions for an anisotropic bulk-based model and get the corresponding
brane-based metric of the model. 相似文献
17.
D. R. K. Reddy P. Govinda Rao R. L. Naidu 《International Journal of Theoretical Physics》2008,47(12):3150-3155
Five dimensional Kaluza-Klein Space-time is considered in the presence of thick domain walls in the scalar-tensor theory formulated
by Brans and Dicke (Phys. Rev. 124:925, 1961). Exact cosmological model, in this theory, is presented with the help of special law of variation proposed by Berman (Nuovo
Cim. B 74:182, 1983) for Hubble’s parameter. Some physical and kinematical properties of the model are also discussed. 相似文献
18.
S. D. Katore R. S. Rane K. S. Wankhade 《International Journal of Theoretical Physics》2010,49(1):187-193
We have studied the evolution of spatially homogeneous and isotropic FRW cosmological model with bulk-viscosity in the frame
work of Barber’s (Gen. Relativ. Gravit. 14: 117, 1982) second self-creation theory of gravitation. The cosmological models are obtained with the help of special law of variation
for Hubble parameter proposed by Bermann (Nuovo Cimento 74B: 182, 1983). Physical parameters of the models have been discussed in case of false vacuum model, Zel’dovich fluid and radiation dominated
fluid. 相似文献
19.
K. S. Adhav M. R. Ugale C. B. Kale M. P. Bhende 《International Journal of Theoretical Physics》2007,46(12):3122-3127
An exact Bianchi type-VI string cosmological model is obtained in a scalar-tensor theory of gravitation proposed by Saez and
Ballester (Phys. Lett. 113:467, 1985). Some physical properties of the model are also discussed. 相似文献
20.
K. S. Adhav A. S. Nimkar M. R. Ugale M. V. Dawande 《International Journal of Theoretical Physics》2008,47(3):634-639
Bianchi type-III space time is considered in the presence of perfect fluid source in the scalar-tensor theory of gravitation
proposed by Brans and Dicke (Phys. Rev. 124:925, 1961). With the help of special law of variation for Hubble’s parameter proposed by Bermann (Nuovo Cimento 74B:182, 1983) a cosmological model with negative constant deceleration parameter is obtained in the presence of perfect fluid with disordered
radiation. Some physical and kinematical properties of the model are also discussed. 相似文献