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1.
Modified Gauss–Bonnet, i.e., f(G) gravity is a possible explanation of dark energy. Late time cosmology for the f(G) gravity non-minimally coupled with a free massless scalar field have been investigated in Ref. [S. Nojiri, S.D. Odintsov, P.V. Tretyakov, Phys. Lett. B 651 (2007) 224, arXiv:0704.2520 [hep-th]; S. Nojiri, S.D. Odintsov, P.V. Tretyakov, Progr. Theor. Phys. Suppl. 172 (2008) 81, arXiv:0710.5232]. In this Letter we generalize the work of Ref. [S. Nojiri, S.D. Odintsov, P.V. Tretyakov, Phys. Lett. B 651 (2007) 224, arXiv:0704.2520 [hep-th]; S. Nojiri, S.D. Odintsov, P.V. Tretyakov, Progr. Theor. Phys. Suppl. 172 (2008) 81, arXiv:0710.5232] by including scalar potential in the matter Lagrangian which is non-minimally coupled with modified Gauss–Bonnet gravity. Also we obtain the conditions for having a much more amazing problem than the acceleration of the universe, i.e. crossing of ω=−1, in f(G) non-minimally coupled with tachyonic Lagrangian. 相似文献
2.
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
3.
D. R. K. Reddy R. L. Naidu B. Satyanarayana 《International Journal of Theoretical Physics》2012,51(10):3222-3227
A five dimensional Kaluza-Klein space-time is considered in the presence of perfect fluid source in f(R,T) gravity proposed by Harko et al. ( [gr-qc], 2011). A cosmological model with a negative constant deceleration parameter with an appropriate choice of a function f(T) is presented. To find a determinate solution of the field equations it is assumed that scalar of expansion is proportional to the shear scalar of the space time. The physical behavior of the model is also studied. 相似文献
4.
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
5.
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
6.
Bruno Baeyens 《Journal of statistical physics》2011,145(6):1640-1648
In a previous article (Baeyens and Verschelde in J. Math. Phys. 36:201, 1995), an improved approach to the scaled particle theory of Reiss et al. was presented. We used a generalized series expansion
of the contact correlation function G(y,r). Truncating it after the third term, we obtained a Padé-like expression for the compressibility factor of the system. That
expression contains two parameters which we were able to calculate, not only for the fluid state, but also for the known glassy
states (Baeyens and Verschelde in Z. Phys. B 102:255, 1997). The resulting equations of state are in good agreement with the simulation data. Yet in the case of the hard sphere crystal
our improved scaled particle theory fails, which is one of the reasons why an extension of it is desirable. 相似文献
7.
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
8.
Building on our earlier work (Misra and Shukla, Nucl. Phys. B 827:112, 2010; Phys. Lett. B 685:347–352, 2010), we show the possibility of generating “light” fermion mass scales of MeV–GeV range (possibly related to the first two generations
of quarks/leptons) as well as eV (possibly related to first two generations of neutrinos) in type IIB string theory compactified
on Swiss-Cheese orientifolds in the presence of a mobile space-time filling D3-brane restricted to (in principle) stacks of fluxed D7-branes wrapping the “big” divisor Σ
B
. This part of the paper is an expanded version of the latter half of Sect. 3 of a published short invited review (Misra,
Mod. Phys. Lett. A 26:1, 2011) written by one of the authors [AM]. Further, we also show that there are no SUSY GUT-type dimension-five operators corresponding
to proton decay, and we estimate the proton lifetime from a SUSY GUT-type four-fermion dimension-six operator to be 1061 years. Based on GLSM calculations in (Misra and Shukla, Nucl. Phys. B 827:112, 2010) for obtaining the geometric K?hler potential for the “big divisor,” using further the Donaldson’s algorithm, we also briefly
discuss in the first of the two appendices the metric for the Swiss-Cheese Calabi–Yau used, which we obtain and which becomes
Ricci flat in the large-volume limit. 相似文献
9.
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
10.
In this paper, we have considered flat Friedmann–Lemaître–Robertson–Walker metric in the framework of perfect fluid models and modified f(G) gravity (where G is the Gauss Bonnet invariant). Particularly, we have considered particular realistic f(G) configurations that could be used to cure finite-time future singularities arising in the late-time cosmic accelerating epochs. We have then developed the viability bounds of these models induced by weak and null energy conditions, by using the recent estimated numerical figures of the deceleration, Hubble, snap and jerk parameters. 相似文献
11.
A. A. Ivanov 《Communications in Mathematical Physics》2011,307(1):1-16
The Majorana representations of groups were introduced in Ivanov (The Monster Group and Majorana Involutions, 2009) by axiomatising some properties of the 2A-axial vectors of the 196 884-dimensional Monster algebra, inspired by the sensational classification of such representations
for the dihedral groups achieved by Sakuma (Int Math Res Notes, 2007). This classification took place in the heart of the theory of Vertex Operator Algebras and expanded earlier results by Miyamoto
(J Alg 268:653–671, 2003). Every subgroup G of the Monster which is generated by its intersection with the conjugacy class of 2A-involutions possesses the (possibly unfaithful) Majorana representation obtained by restricting to G the action of the Monster on its algebra. This representation of G is said to be based on an embedding of G in the Monster. So far the Majorana representations have been classified for the groups G isomorphic to the symmetric group S
4 of degree 4 (Ivanov et al. in J Alg 324:2432–2463, 2010), the alternating group A
5 of degree 5 (Ivanov AA, Seress á in Majorana Representations of A
5, 2010), and the general linear group GL
3(2) in dimension 3 over the field of two elements (Ivanov AA, Shpectorov S in Majorana Representations of L
3(2), 2010). All these representations are based on embeddings in the Monster of either the group G itself or of its direct product with a cyclic group of order 2. The dimensions and shapes of these representations are given
in the following table: 相似文献
12.
A simple model for the dynamics of the Magellanic Stream (MS), in the framework of modified gravity models is investigated.
We assume that the galaxy is made up of baryonic matter out of context of dark matter scenario. The model we used here is
named Modified Gravity (MOG) proposed by Moffat (J. Cosmol. Astropart. Phys. 003, 2005). In order to examine the compatibility of the overall properties of the MS under the MOG theory, the observational radial
velocity profile of the MS is compared with the numerical results using the χ
2 fit method. In order to obtain the best model parameters, a maximum likelihood analysis is performed. We also compare the
results of this model with the Cold Dark Matter (CDM) halo model and the other alternative gravity model that proposed by
Bekenstein (Phys. Rev. D 70:083509, 2004), so called TeVeS. We show that by selecting the appropriate values for the free parameters, the MOG theory seems to be plausible
to explain the dynamics of the MS as well as the CDM and the TeVeS models. 相似文献
13.
Anindita Banerjee Kamal Patel Anirban Pathak 《International Journal of Theoretical Physics》2011,50(2):507-510
Recently Yang et al. (Int. J. Theor. Phys. 48:516, 2009) have shown that an unknown qubit can be teleported by using a particular GHZ-like state as quantum channel. However, there are several errors in the calculation which lead to incorrect conclusions. The errors
have been indicated and corrected. It is also noted that their scheme and the independently proposed teleportation scheme
of Zhang et al. (Int. J. Theor. Phys. 48:3331, 2009) uses quantum channel from the same family and any state of that family may be used for teleportation. 相似文献
14.
A. Banijamali M. R. Setare B. Fazlpour 《International Journal of Theoretical Physics》2011,50(10):3275-3283
We construct a holographic dark energy density in the modified gravity for a non-flat space. We incorporate possible modification
of equation of state for the holographic energy density in the spirit of f(R) gravity. In this case we choose Jeans length as the IR cut-off in the holographic model. Then we employ the non-flat universe
for the holographic modified gravity to obtain a general form of f(R) in this setup. 相似文献
15.
Recently, much research has indicated that more and more cancers pose a threat to human life. Cancers are caused by oncogenes. Many human oncogenes have been found and most of them are located on chromosomes. The discovery of the oncogene plays a significant role in the treatment of cancer. The p53 tumor suppressor gene has received much attention because it frequently mutates or deletes in tumor cells of most people. Thus, the study of oncogenes is significant. In order to establish the Galois field (GF(7)), the indefinite gene is introduced as D and oncogene is introduced as O, and P. Taking the polynomial coefficients a0, a1, a2 ∈ GF(7) and the bijective function f:GF(7) → {D,A,C,O,G,T,P}, where f(0) = D, f(1) = A, f(2) = C, f(3) = O, f(4) = G, f(5) = T, and f(6) = P, the bijective φ may be written as φ(a0 + a1x + a2x2). Based on the algebraic structure, we can not only analyse the DNA sequence of oncogenes, but also predict possible new cancers. 相似文献
16.
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
17.
M. R. Setare J. Sadeghi A. Banijamali 《The European Physical Journal C - Particles and Fields》2009,64(3):433-438
In this paper we show that power-law inflation can be realized in non-minimal gravitational coupling of electromagnetic field
with a general function of the Gauss–Bonnet invariant. Such a non-minimal coupling may appear due to quantum corrections.
We also consider modified Maxwell-F(G) gravity in which non-minimal coupling between electromagnetic field and f(G) occurs in the framework of modified Gauss–Bonnet gravity. It is shown that inflationary cosmology and late-time accelerated
expansion of the universe are possible in such a theory. 相似文献
18.
Generalized from the so-called teleparallel gravity, which is exactly equivalent to general relativity, f(T) gravity has been proposed as an alternative gravity model to account for the dark energy phenomena. In this letter we prove
that the external vacuum gravitational field for a spherically symmetric distribution of source matter in the f(T) gravity framework must be static. The conclusion is independent of the radial distribution and spherically symmetric motion
of the source matter, that is, whether it is in motion or static. As a consequence, the Birkhoff’s theorem is valid in the
general nonsingular f(T) theory at the un-perturbative level. We also discuss its application in the de Sitter spacetime evolution phase as preferred
by present dark energy observations. 相似文献
19.
The regularized determinant of the Paneitz operator arises in quantum gravity [see Connes in (Noncommutative geometry, 1994), IV.4.γ]. An explicit formula for the relative determinant of two conformally related metrics was computed by Branson in (Commun Math Phys 178:301–309, 1996). A similar formula holds for Cheeger’s half-torsion, which plays a role in self-dual field theory [see Juhl in (Families of conformally covariant differential operators, q-curvature and holography. Progress in Mathematics, vol 275, 2009)], and is defined in terms of regularized determinants of the Hodge laplacian on p-forms (p < n/2). In this article we show that the corresponding actions are unbounded (above and below) on any conformal four-manifold. We also show that the conformal class of the round sphere admits a second solution which is not given by the pull-back of the round metric by a conformal map, thus violating uniqueness up to gauge equivalence. These results differ from the properties of the determinant of the conformal Laplacian established in (Commun Math Phys 149:241–262, 1992), (Ann Math 142:171–212, 1995), (Commun Math Phys 189:655–665, 1997). 相似文献
20.
M. F. Shamir 《Journal of Experimental and Theoretical Physics》2016,123(4):607-616
We discuss dark-energy cosmological models in f(G) gravity. For this purpose, a locally rotationally symmetric Bianchi type I cosmological model is considered. First, exact solutions with a well-known form of the f(G) model are explored. One general solution is discussed using a power-law f(G) gravity model and physical quantities are calculated. In particular, Kasner’s universe is recovered and the corresponding f(G) gravity models are reported. Second, the energy conditions for the model under consideration are discussed using graphical analysis. It is concluded that solutions with f(G) = G5/6 support expansion of universe while those with f(G) = G1/2 do not favor the current expansion. 相似文献