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1.
We reconsider the issue of cosmological dynamics in a DGP setup with a bulk scalar field. The ghost-free, normal branch of
this DGP-inspired braneworld scenario has the potential to realize a self-consistent phantom-like behavior. The roles played
by the bulk canonical scalar field on this phantom-like dynamics are explored. Within a dynamical system approach, the effective
phantom nature of the scenario is investigated with details. This analysis shows that there is a stable, late-time de Sitter
phase. 相似文献
2.
Malihe Heydari-Fard 《Astrophysics and Space Science》2010,325(2):287-292
Using the effective gravitational field equations in the warped DGP brane-world scenario (Maeda et al. in Phys. Rev. D 68:024033,
2003), we study spherically symmetric vacuum (static black hole) solutions on the brane. Working with a conformally flat bulk,
we have obtained an exact Schwarzschild–de Sitter black hole solution similar to the standard solution in the presence of
a cosmological constant, which confirms the idea that an extra term in the effective vacuum field equations on the warped
DGP brane can play the role of a positive cosmological constant. 相似文献
3.
We consider cosmological dynamics of a canonical bulk scalar field, which is coupled non-minimally to 5-dimensional Ricci scalar in a DGP setup. We show that presence of this non-minimally coupled bulk scalar field affects the jump conditions of the original DGP model significantly. Within a superpotential approach, we perform some numerical analysis of the model parameter space and consider bulk-brane energy exchange in this setup. Also we show that the normal, ghost-free branch of the DGP solutions in this case has the potential to realize a self-consistent phantom-like behavior and therefore explains late time acceleration of the universe in a consistent way. 相似文献
4.
We consider the cosmological dynamics of a tachyon field localized on the extended DGP braneworld scenario. We present a detailed analysis of the critical points in the phase space of the model, their stability and late-time cosmological viability of the solutions. We study the luminosity distance behavior of this ?EDGP model and compare it with ΛCDM model. Also we show that the EDGP solutions in the presence of tachyon field can explain late time acceleration of the universe. 相似文献
5.
As a generalization of the Brans-Dicke type scalar-tensor gravity in a braneworld context, we study cosmological phase space of a braneworld model with induced gravity in the presence of a scalar field on the brane. We consider a quintom field minimally or non-minimally coupled to induced gravity on the warped DGP brane and we present a detailed analysis of the critical points, their stability and late-time cosmological viability of the solutions within a phase space approach. In particular, de Sitter solutions, different from the famous self-accelerated branch of the DGP model are found and the phase-space analysis for checking their attractor properties is performed. We analyze also the possibility of crossing of the phantom divide by the effective equation of state parameter of the model. We also focus on the classical stability of the solutions in w–w′ phase plane. 相似文献
6.
In this paper we compare outcomes of some extended phantom-like cosmologies with each other and also with ΛCDM and ΛDGP. We
focus on the variation of the luminosity distances, the age of the universe and the deceleration parameter versus the redshift
in these scenarios. In a dynamical system approach, we show that the accelerating phase of the universe in the f(R)-DGP scenario is stable if one consider the curvature fluid as a phantom scalar field in the equivalent scalar-tensor theory, otherwise it is a transient and unstable phenomenon. Up
to the parameters values adopted in this paper, the extended F(R,ϕ)-DGP scenario is closer to the ΛCDM scenario than other proposed models. All of these scenarios explain the late-time cosmic
speed-up in their normal DGP branches, but the redshift at which transition to the accelerating phase occurs are different:
while the ΛDGP model transits to the accelerating phase much earlier, the F(R,ϕ)-DGP model transits to this phase much later than other scenarios. Also, within the parameter spaces adopted in this paper,
the age of the universe in the f(R)-DGP model is larger than ΛCDM, but this age in F(G,ϕ)-DGP is smaller than ΛCDM. 相似文献
7.
We study the late-time cosmological viability of the solutions in the DGP braneworld scenario. We consider a quintessence field trapped on the normal branch of the DGP model and we suppose this scalar field is both minimally and non-minimally coupled to induced gravity on the brane. Since a successful cosmological model should therefore admit for a sequence of epochs: a radiation era, a sufficiently long matter dominated era and a final stable positively accelerated scaling solution, we analyze the cosmological properties of system in its critical points. 相似文献
8.
K. Saaidi H. Sheikhahmadi T. Golanbari S. W. Rabiei 《Astrophysics and Space Science》2013,348(1):233-240
We study the holographic dark energy (HDE) model in generalized Brans-Dicke scenario with a non-minimal coupling between the scalar field and matter Lagrangian namely Chameleon Brans Dicke (CBD) mechanism. In this study we consider the interacting and non-interacting cases for two different cutoffs. The physical quantities of the model such as, equation of state (EoS) parameter, deceleration parameter and the evolution equation of dimensionless parameter of dark energy are obtained. We shall show that this model can describe the dynamical evolution of fraction parameter of dark energy in all epochs. Also we find the EoS parameter can cross the phantom divide line by suitable choices of parameters without any mines kinetic energy term. 相似文献
9.
A version of the virial theorem is derived in a brane-world scenario in the framework of a warped DGP model where the action on the brane is an arbitrary function of the Ricci scalar, $\mathcal{L}(R)$ . The extra terms in the modified Einstein equations generate an equivalent mass term (geometrical mass), which give an effective contribution to the gravitational energy and offer viable explanation to account for the virial mass discrepancy in clusters of galaxies. We also obtain the radial velocity dispersion of galaxy clusters and show that it is compatible with the radial velocity dispersion profile of such clusters. Finally, we compare the result of the model with $\mathcal{L}(R)$ gravity theories. 相似文献
10.
11.
12.
The bounce with non-minimal coupling is very interesting topic because in the early time, general relativity is likely to
be modified, which can give some valuable effects to the evolution of our universe. In this paper we introduce a string-inspired
model for bouncing universe, utilizing the tachyon field as well as contributions from general non-minimal kinetic couplings
and curvature. It is shown numerically that the bouncing solution appears in the model whereas the equation of state (EoS)
parameter crosses the phantom divider. 相似文献
13.
It has been recently shown that tachyonic chameleon model of dark energy in which tachyon scalar field non-minimally coupled to the matter admits stable scaling attractor solution that could give rise to the late-time accelerated expansion of the universe and hence alleviate the coincidence problem. In the present work, we use data from Type Ia supernova (SN Ia) and Baryon Acoustic oscillations to place constraints on the model parameters. In our analysis we consider in general exponential and non-exponential forms for the non-minimal coupling function and tachyonic potential and show that the scenario is compatible with observations. 相似文献
14.
Prabir Rudra 《Astrophysics and Space Science》2012,342(2):579-599
In this work we explore the background dynamics when dark energy is coupled to dark matter with a suitable interaction in the universe described by brane cosmology. Here DGP and the RSII brane models have been considered separately. Dark energy in the form of Generalized Cosmic Chaplygin gas is considered. A suitable interaction between dark energy and dark matter is considered in order to at least alleviate (if not solve) the cosmic coincidence problem. The dynamical system of equations is solved numerically and a stable scaling solution is obtained. A significant attempt towards the solution of the cosmic coincidence problem is taken. The statefinder parameters are also calculated to classify the dark energy models. Graphs and phase diagrams are drawn to study the variations of these parameters. It is also seen that the background dynamics of Generalized Cosmic Chaplygin gas is consistent with the late cosmic acceleration, but not without satisfying certain conditions. It has been shown that the universe in both the models follows the power law form of expansion around the critical point, which is consistent with the known results. Future singularities were studied and our models were declared totally free from any types of such singularities. Finally, some cosmographic parameters were also briefly studied. Our investigation led to the fact that although Generalized cosmic Chaplygin gas with a far lesser negative pressure compared to other dark energy models, can overcome the relatively weaker gravity of RS II brane, with the help of the negative brane tension, yet for the DGP brane model with much higher gravitation, the incompetency of Generalized cosmic Chaplygin gas is exposed, and it cannot produce the accelerating scenario until it reaches the phantom era. 相似文献
15.
G. I. Ogilvie 《Monthly notices of the Royal Astronomical Society》2006,365(3):977-990
The non-linear dynamics of a warped accretion disc is investigated in the important case of a thin Keplerian disc with negligible viscosity and self-gravity. A one-dimensional evolutionary equation is formally derived that describes the primary non-linear and dispersive effects on propagating bending waves other than parametric instabilities. It has the form of a derivative non-linear Schrödinger (DNLS) equation with coefficients that are obtained explicitly for a particular model of a disc. The properties of this equation are analysed in some detail and illustrative numerical solutions are presented. The non-linear and dispersive effects both depend on the compressibility of the gas through its adiabatic index Γ. In the physically realistic case Γ < 3, non-linearity does not lead to the steepening of bending waves but instead enhances their linear dispersion. In the opposite case Γ > 3, non-linearity leads to wave steepening and solitary waves are supported. The effects of a small effective viscosity, which may suppress parametric instabilities, are also considered. This analysis may provide a useful point of comparison between theory and numerical simulations of warped accretion discs. 相似文献
16.
Ahmad Rami El-Nabulsi 《Astrophysics and Space Science》2010,327(1):111-115
We investigate five-dimensional Brans–Dicke cosmology with spacetime described by the homogeneous, anisotropic and flat spacetime
with the topology M
1×R
3×S
1 where S
1 is taken in the form of a circle. We conjecture throughout this letter that the extra-dimension compactifies as the visible
dimensions expand like b(t)≈a
−1(t) and that the non-minimal coupling between the scalar field and the matter is of the form f(φ)∝
φ
2. The model gives rise to a transition from a decelerated epoch to an accelerated epoch for large values of the Brans–Dicke
parameter ω. The model predicts crossing of the phantom divided barrier unless the universe is governed by a growing matter field. 相似文献
17.
In this paper it is shown that in non-minimally coupled Brans-Dicke theory containing a self-interacting potential, a suitable conformal transformation can automatically give rise to an interaction between the normal matter and the Brans-Dicke scalar field. Considering the scalar field in the Einstein frame as the quintessence matter, it has been shown that such a non-minimal coupling between the matter and the scalar field can give rise to a late time accelerated expansion for the universe preceded by a decelerated expansion for very high values of the Brans-Dicke parameter ω. We have also studied the observational constraints on the model parameters considering the Hubble and Supernova data. 相似文献
18.
Teleparallel gravity is an equivalent formulation of general relativity in which instead of the Ricci scalar R, one uses the torsion scalar T for the Lagrangian density. Recently teleparallel dark energy has been proposed by Geng et al. (in Phys. Lett. B 704, 384, 2011). They have added quintessence scalar field, allowing also a non-minimal coupling with gravity in the Lagrangian of teleparallel gravity and found that such a non-minimally coupled quintessence theory has a richer structure than the same one in the frame work of general relativity. In the present work we are interested in tachyonic teleparallel dark energy in which scalar field is responsible for dark energy in the frame work of torsion gravity. We find that such a non-minimally coupled tachyon gravity can realize the crossing of the phantom divide line for the effective equation of state. Using the numerical calculations we display such a behavior of the model explicitly. 相似文献
19.
Claudia del P. Lagos Nelson D. Padilla Sofía A. Cora 《Monthly notices of the Royal Astronomical Society》2009,395(2):625-636
We use a combination of a cosmological N -body simulation of the concordance Λ cold dark matter paradigm and a semi-analytic model of galaxy formation to investigate the spin development of central supermassive black holes (BHs) and its relation to the BH host galaxy properties. In order to compute BH spins, we use the α model of Shakura & Sunyaev and consider the King et al. warped disc alignment criterion. The orientation of the accretion disc is inferred from the angular momentum of the source of accreted material, which bears a close relationship to the large-scale structure in the simulation. We find that the final BH spin depends almost exclusively on the accretion history and only weakly on the warped disc alignment. The main mechanisms of BH spin-up are found to be gas cooling processes and disc instabilities, a result that is only partially compatible with Monte Carlo models where the main spin-up mechanisms are major mergers and disc instabilities; the latter results are reproduced when implementing randomly oriented accretion discs in our model. Regarding the BH population, we find that more massive BHs, which are hosted by massive ellipticals, have higher spin values than less massive BHs, hosted by spiral galaxies. We analyse whether gas accretion rates and BH spins can be used as tracers of the radio loudness of active galactic nuclei (AGN). We find that the current observational indications of an increasing trend of radio-loud AGN fractions with stellar and BH mass can be easily obtained when placing lower limits on the BH spin, with a minimum influence from limits on the accretion rates; a model with random accretion disc orientations is unable to reproduce this trend. Our results favour a scenario where the BH spin is a key parameter to separate the radio-loud and radio-quiet galaxy populations. 相似文献
20.
In this paper we examine the recently introduced Dvali-Gabadadze-Porrati (DGP) gravity model. We use a space-time metric in which the local gravitation source dominates the metric over the contributions from the cosmological flow. Anticipating ideal possible solar system effects, we derive expressions for the signal time delays in the vicinity of the Sun. and for various ranges of the angle θ of the signal approach, The time contribution due to DGP correction to the metric is found to be proportional to b 3/2/c 2 r 0. For r 0 equal to 5 Mpc and θ in the range [−π/3,π/3], Δt is equal to 0.0001233 ps. This delay is extremely small to be measured by today’s technology but it could be probably measurable by future experiments. 相似文献