共查询到20条相似文献,搜索用时 31 毫秒
1.
Hossein Farajollahi Mehrdad Farhoudi Hossein Shojaie 《International Journal of Theoretical Physics》2010,49(10):2558-2568
We study longstanding problem of cosmological clock in the context of Brans–Dicke theory of gravitation. We present the Hamiltonian
formulation of the theory for a class of spatially homogeneous cosmological models. Then, we show that formulation of the
Brans–Dicke theory in the Einstein frame allows how an identification of an appropriate cosmological time variable, as a function
of the scalar field in the theory, can be emerged in quantum cosmology. The classical and quantum results are applied to the
Friedmann–Robertson–Walker cosmological models. 相似文献
2.
José Edgar Madriz Aguilar Carlos Romero Adriano Barros 《General Relativity and Gravitation》2008,40(1):117-130
We investigate, in the context of five-dimensional (5D) Brans–Dicke theory of gravity, the idea that macroscopic matter configurations
can be generated from pure vacuum in five dimensions, an approach first proposed by Wesson and collaborators in the framework
of 5D general relativity. We show that the 5D Brans–Dicke vacuum equations when reduced to four dimensions (4D) lead to a
modified version of Brans–Dicke theory in 4D. As an application of the formalism, we obtain two 5D extensions of 4D O’Hanlon
and Tupper vacuum solution and show that they lead two different cosmological scenarios in 4D. 相似文献
3.
Effects of a 4d dilaton field on a falling test mass are examined from the Einstein frame perspective of scalar-tensor theory.
Results are obtained for the centripetal acceleration of particles in circular orbits, and the radial acceleration for particles
with pure radial motion. These results are applied to the specific case of nonrelativistic motion in the weak field approximation
of Brans–Dicke theory, employing the exact Xanthopoulos–Zannias solutions. For a given parameter range, the results obtained
from Brans–Dicke theory are qualitatively dramatically different from those of general relativity. Comments are made concerning
a comparison with the general relativistic results in the limit of an infinite Brans–Dicke parameter. 相似文献
4.
Yousef Bisabr 《General Relativity and Gravitation》2012,44(2):427-435
We consider Brans–Dicke theory with a self-interacting potential in Einstein conformal frame. We show that an accelerating
expansion is possible in a spatially flat universe for large values of the Brans–Dicke parameter consistent with local gravity
experiments. 相似文献
5.
Ahmad Rami El-Nabulsi 《General Relativity and Gravitation》2010,42(8):1875-1887
The study of Brans–Dicke cosmology has attracted considerable attention in the recent years since it explains most of the
important features of the progress of the universe. We discuss in this letter a homogeneous and anisotropic cosmological model
in the framework of Brans–Dicke theory including together a non-linear derivative interaction which appears in theory with
the Galilean shift symmetry, a Gauss–Bonnet invariant motivated from heterotic string theory which plays an important role
in numerous alternatives cosmological frameworks, two scalar fields and their interactions to fit easier with universe history
expansion. Several particular cases are studied and the properties related to scaling solutions and asymptotic behaviour are
discussed in some details. 相似文献
6.
We investigate cylindrically symmetric vacuum solutions with both null and non-null electromagnetic fields in the framework
of the Brans–Dicke theory and compare these solutions with some of the well-known solutions of general relativity for special
values of the parameters of the resulting field functions. We see that, unlike general relativity where the gravitational
force of an infinite and charged line mass acting on a test particle is always repulsive, it can be attractive or repulsive
for Brans–Dicke theory depending on the values of the parameters as well as the radial distance from the symmetry axis. 相似文献
7.
Hossein Ghaffarnejad 《General Relativity and Gravitation》2008,40(10):2229-2239
Using some suitable combinations of a dynamical unit time-like four-velocity of a preferred reference frame, Ricci tensor
and covariant derivatives of the Brans–Dicke (BD) scalar field, we propose a new scalar–vector–tensor gravity model in which
an Euclidean Jordan–Brans–Dicke (JBD) action is reduced to its Lorentzian version with no used complex coordinates. Thus it
should be play an important role in the process of metric signature transition of a suitable dynamical curved space-time.
In this work we follow the ideas proposed by Barbero et al. As an application of the model, we study a classical perfect fluid
cosmological universe described in a flat Robertson–Walker background metric. Mathematical derivations of the equations predict
a non-singular scale factor for the space-time in the both of dust and radiation dominated states where value of the Brans–Dicke
parameter is fixed, but there is still an arbitrary parameter which should be determined by the boundary values of the cosmological
system. Furthermore its classical cosmological vacuum solutions is obtained as a non-singular model with a fixed Brans–Dicke
parameter. Although there is obtained a singular perfect fluid cosmological solution which may not be suitable, because in
this case the Brans–Dicke parameter is not still fixed. 相似文献
8.
M.C.B. Abdalla M.E.X. Guimarães J.M. Hoff da Silva 《The European Physical Journal C - Particles and Fields》2008,55(2):337-342
We apply the Gauss–Codazzi formalism to brane-worlds within the framework of Brans–Dicke gravity. The compactification is
taken from six to five dimensions in order to formalize brane-world models with hybrid compactification in scalar tensor theories.
PACS 04.50.+h; 98.80.Cq 相似文献
9.
Hui-Qing Lu Li-Ming Shen Guo-Hong Yang Y. Y. Lai K. S. Cheng 《International Journal of Theoretical Physics》2002,41(5):939-951
We apply the theory developed in quantum cosmology to a model of charged generalized Brans–Dicke gravity. This is a quantum model of gravitation interacting with a charged Brans–Dicke type scalar field which is considered in the Pauli frame. The Wheeler–DeWitt equation describing the evolution of the quantum Universe is solved in the semiclassical approximation by applying the WKB approximation. The wave function of the Universe is also obtained by applying both the Vilenkin-like and the Hartle–Hawking-like boundary conditions. We then make predictions from the wave functions and infer that the Vilenkin's boundary condition is more reasonable in the Brans–Dicke gravity models leading a large vacuum energy density at the beginning of the inflation. 相似文献
10.
K. S. Adhav A. S. Nimkar R. P. Holey 《International Journal of Theoretical Physics》2007,46(10):2396-2400
For a string Bianchi type-I metric of Kasner form in Brans–Dicke theory of gravity, it is not possible to describe an anisotropic
physical model of the universe. 相似文献
11.
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
12.
13.
Motivated by a recent work of one of us (Sheykhi in Phys Rev D 81: 023525, 2010), we extend it by using quantum (or entropy)
corrected new agegraphic dark energy in the Brans–Dicke cosmology. The correction terms are motivated from the loop quantum
gravity which is one of the competitive theories of quantum gravity. Taking the non-flat background spacetime along with the
conformal age of the universe as the length scale, we derive the dynamical equation of state of dark energy and the deceleration
parameter. An important consequence of this study is the phantom divide scenario with entropy-corrected new agegraphic dark
energy. Moreover, we assume a system of dark matter, radiation and dark energy, while the later interacts only with dark matter.
We obtain some essential expressions related with dark energy dynamics. The cosmic coincidence problem is also resolved in
our model. 相似文献
14.
The role that the auxiliary scalar field φ plays in Brans–Dicke cosmology is discussed. If a constant vacuum energy is assumed
to be the origin of dark energy, then the corresponding density parameter would be a quantity varying with φ; and almost all
of the fundamental components of our universe can be unified into the dynamical equation for φ. As a generalization of Brans–Dicke
theory, we propose a new gravity theory with a complex scalar field ϕ which is coupled to the cosmological curvature scalar.
Through such a coupling, the Higgs mechanism is naturally incorporated into the evolution of the universe, and a running density
of the field vacuum energy is obtained which may release the particle standard model from the rigorous cosmological constant
problem in some sense. Our model predicts a running mass scale of the fundamental particles in which the gauge symmetry breaks
spontaneously. The running speed of the mass scale in our case could survive all existing experiments. 相似文献
15.
J. R. Morris 《General Relativity and Gravitation》2012,44(2):437-448
Static spherically symmetric solutions of 4d Brans–Dicke theory include a set of naked singularity solutions. Dilatonic effects
near the naked singularities result in either a shielding or an antishielding effect from intruding massive test particles.
One result is that for a portion of the solution parameter space, no communication between the singularity and a distant observer
is possible via massive particle exchanges. Kaluza–Klein gravity is considered as a special case. 相似文献
16.
Brans–Dicke scalar–tensor theory provides a conformal coupling of the scalar field with gravity in Einstein’s frame. This
model is equivalent to an interacting quintessence in which dark matter is coupled to dark energy. This provides a natural
mechanism to alleviate the coincidence problem. We investigate the dynamics of this model and show that it leads to comparable
dark energy and dark matter densities today. 相似文献
17.
S. Habib Mazharimousavi M. Halilsoy Z. Amirabi 《General Relativity and Gravitation》2010,42(2):261-280
We find large classes of non-asymptotically flat Einstein–Yang–Mills–Dilaton and Einstein–Yang–Mills–Born–Infeld–Dilaton black
holes in N-dimensional spherically symmetric spacetime expressed in terms of the quasilocal mass. Extension of the dilatonic
YM solution to N-dimensions has been possible by employing the generalized Wu-Yang ansatz. Another metric ansatz, which aided
in finding exact solutions is the functional dependence of the radius function on the dilaton field. These classes of black
holes are stable against linear radial perturbations. In the limit of vanishing dilaton we obtain Bertotti–Robinson type metrics
with the topology of AdS
2×S
N–2. Since connection can be established between dilaton and a scalar field of Brans–Dicke type we obtain black hole solutions
also in the Brans–Dicke–Yang–Mills theory as well. 相似文献
18.
V. V. Obukhov K. E. Osetrin A. E. Filippov Yu. A. Rybalov 《Russian Physics Journal》2009,52(2):170-175
A problem of classification of the conformally flat St?ckel spaces admitting complete separation of variables in the Hamilton–Jacobi
equation is studied within the framework of the Brans–Dicke scalar-tensor gravitational theory. Solutions to the field equations
of the theory are found for the conformally flat St?ckel spaces of type (1.1), and explicit forms of the metric and scalar
field are presented.
Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 54–58, February, 2009. 相似文献
19.
This paper is devoted to study Bianchi type I cosmological model in Brans–Dicke theory with self-interacting potential by
using perfect, anisotropic and magnetized anisotropic fluids. We assume that the expansion scalar is proportional to the shear
scalar and also take a power law ansatz for the scalar field. The physical behavior of the resulting models are discussed
through different parameters. We conclude that contrary to the universe model, the anisotropic fluid approaches isotropy at
later times in all cases, which is consistent with observational data. 相似文献
20.
We show that primordial black holes can be formed in the matter-dominated era with gravity described by the Brans–Dicke theory.
Considering an early matter-dominated era between inflation and reheating, we found that the primordial black holes formed
during that era evaporate at a quicker rate than those of early radiation-dominated era. Thus, in comparison with latter case,
less number of primordial black holes could exist today. Again the constraints on primordial black hole formation tend towards
the larger value than their radiation-dominated era counterparts indicating a significant enhancement in the formation of
primordial black holes during the matter-dominaed era. 相似文献