共查询到20条相似文献,搜索用时 171 毫秒
1.
Subenoy Chakraborty Tapan Kumar Ghosh 《International Journal of Theoretical Physics》1998,37(9):2409-2413
We develop string cosmology in the presence ofa Brans–Dicke (BD) scalar field coupled toEinstein gravity for higher dimensional space-time.Solutions are obtained for the equation of state for thep-string, and physical situations arediscussed. 相似文献
2.
The five-dimensional Brans–Dicke theory naturally provides two scalar fields by the Killing reduction mechanism. These two scalar fields could account for the accelerated expansion of the universe. We test this model and constrain its parameter by using the type Ia supernova (SN Ia) data. We find that the best fit value of the 5-dimensional Brans–Dicke coupling constant is ω=−1.9. This result is also consistent with other observations such as the baryon acoustic oscillation (BAO). 相似文献
3.
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
4.
We present a suggestion on the interpretation of canonical time evolution when gravitation is present, based on the nonlinear gauge approach to gravity. Essentially, our proposal consists of an internal-time concept, with the time variable taken from the dynamical fields characteristic of the nonlinear realization of the internal time-translational symmetry. Physical time evolution requires the latter symmetry to be broken. After disregarding other breaking mechanisms, we appeal to the Jordan–Brans–Dicke action, conveniently interpreted, to achieve that goal. We show that nontrivial time evolution follows, the special relativistic limit being recovered in the absence of gravity. 相似文献
5.
The Bruns–Dicke theory with a scalar field related to the quantum spinor matter is discussed [1]. The quantum Friedmann cosmology is studied. A solution to the equations of motion describing the quantum Friedmann Universe is examined for stability for the case of a flat model of the Universe. A different exact analytical solution to these equations is derived. 相似文献
6.
We study a cosmological implication of holographic dark energy in the Brans–Dicke gravity. We employ the holographic model of dark energy to obtain the equation of state for the holographic energy density in non-flat (closed) universe enclosed by the event horizon measured from the sphere of horizon named L. Our analysis shows that one can obtain the phantom crossing scenario if the model parameter α (of order unity) is tuned accordingly. Moreover, this behavior is achieved by treating the Brans–Dicke scalar field as a Chameleon scalar field and taking a non-minimal coupling of the scalar field with matter. Hence one can generate phantom-like equation of state from a holographic dark energy model in non-flat universe in the Brans–Dicke cosmology framework. 相似文献
7.
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
8.
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
9.
Using scaled variables we are able to integrate an equation valid for isotropic and anisotropic Bianchi type I, V, IX models in Brans–Dicke (BD) theory. We analyze known and new solutions for these models in relation with the possibility that anisotropic models asymptotically isotropize, and/or possess inflationary properties. In particular, a new solution of curved (k 0) Friedmann–Robertson–Walker (FRW) cosmologies in Brans–Dicke theory is analyzed. 相似文献
10.
B. Carter 《International Journal of Theoretical Physics》2002,41(11):2201-2210
In contrast with pseudo-gravitational effects that are mathematically analogous but physically quite distinct from gravity, this presentation deals with a kind of quasi-gravitational effect that can act in an asymmetrically moving brane worldsheet in a manner that approximates (and in a crude analysis might be physically indistinguishable from) the effect that would arise from genuine gravitation, of ordinary Newtonian type in nonrelativistic applications and of scalar–tensor (Jordan–Brans–Dicke rather than pure Einstein) type in relativistic applications. 相似文献
11.
12.
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
13.
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
14.
This Letter is a study of the effects of higher dimensional gravity and Brans–Dicke (BD) scalar field on cosmic acceleration in 5-D BD cosmological model. We assume a flat cosmological model in which the matter content of the universe is either cold dark matter or radiation. In a framework to study attractor solutions in the phase space we simultaneously constrain the model parameters with the observational data for distance modulus. The phase space analysis illustrates that the universe begins from an unstable state in the past and eventually reaches an asymptotically stable state (attractor). We examine the model by performing Hubble parameter test in addition to statefinder diagnosis. We also reconstruct the equation of state parameter, the scale factor in 3-D space and along extra dimension. The results show that due to the presence of extra dimension and Brans–Dicke scalar field in the model, the universe undergoes a period of acceleration. 相似文献
15.
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
16.
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
17.
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
18.
V. Ya. Demikhovskii D. I. Kamenev G. A. Luna-Acosta 《Radiophysics and Quantum Electronics》1995,38(3-4):151-156
We study the quantum dynamics of a charged particle rotating in a constant magnetic field and in the field of a monochromatic wave propagating perpendicular to the magnetic field under the condition of cyclotron resonance. Quasienergies and quasienergy functions are numerically calculated in the resonance approximation. The passage to the limit from the quantum model to the classical one is discussed.Lobachevskii State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 38, No. 3-4, pp. 232–240, March–April, 1995. 相似文献
19.
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
20.
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