Crossing w = -1 in Gauss-Bonnet Brane World with Induced Gravity

Recent type Ia supernovas data seemingly favor a dark energy model whose equation of state w(z) crosses -1 very recently, which is a much more amazing problem than the acceleration of the universe. In this paper we show that it is possible to realize such a crossing without introducing any phantom component in a Gauss-Bonnet brane world with induced gravity, where a four-dimensional curvature scalar on the brane and a five-dimensional Gauss-Bonnet term in the bulk are present. In this realization, the Gauss-Bonnet term and the mass parameter in the bulk play a crucial role.     

Abundance of Asymmetric Dark Matter in Brane World Cosmology

Relic abundance of asymmetric Dark Matter particles in brane world cosmological scenario is investigated in this article. Hubble expansion rate is enhanced in brane world cosmology and it affects the relic abundance of asymmetric Dark Matter particles. We analyze how the relic abundance of asymmetric Dark Matter is changed in this model. We show that in such kind of nonstandard cosmological scenario, indirect detection of asymmetric Dark Matter is possible if the cross section is small enough which let the anti-particle abundance kept in the same amount with the particle. We show the indirect detection signal constraints can be used to such model only when the cross section and the 5-dimensional Planck mass scale are in appropriate values.     

Phantom Divide Crossing on Brane World

We study the RSII brane world corrected by the four-dimensional scalar curvature and five-dimensional Gauss-Bonnet curvature. The energy transfer between brane and bulk is also taken into account. Parameterizing the energy transfer, the resulting Friedmann equation on brane is solved at low energy. It is shown that phantom divide crossing may be achieved in the braneworld model with wide possibilities, embodying the combined effect of brane-bulk energy transfer, curvature corrections, and the fine-turning mechanics.     

Null Geodesics in Brane World Scenarios

We study the null bulk geodesic motion in the brane world inwhich the bulk metric has an un-stabilized extra spatial dimension.We find that the null bulk geodesic motion as observed on the3-brane with Z₂ symmetry would be a timelike geodesic motioneven though there exists an extra non-gravitational force incontrast with the case of the stabilized extra spatial dimension.In other words the presence of the extra non-gravitational forcewould not violate the Z₂ symmetry.     

Coleman–de Luccia Instanton of the Second Order in a Brane World

The second order Coleman–de Luccia instanton and its action in the Randall–Sundrum type II model are investigated and the comparison with the results in Einstein’s general relativity is done in the present paper. PACS Numbers: 98.80.Cq.     

The Complete Brane Solution in D-Dimensional Coupled Gravity System

We present the complete explicit brane solution in D-dimensional coupled gravity system.     

A Study of Brane Solutions in D-Dimensional Coupled Gravity System

We use only the equation.of motion for an interacting system of gravity, dilaton and antisymmetric tensor to study the soliton solutions by making use of a Poincaré-invariant ansatz. We show that the system of equations is completely integrable and the solution is unique with appropriate boundary conditions. Some new classes of solutions are also given explicitly.     

Phantom-Like Effects on Warped DGP Brane

We study phantom-like effect on the DGP brane embedded in a five-dimensional AdS bulk. We show that this effect can be realized without phantom matter on this warped DGP brahe. We investigate the role played by the bulk cosmological constant on the phantom-like effect on the brane and we show that it tends to reduce this effect. Also, warped compactification of the bulk manifold increases the values of the effective and total equation of state parameters of the model relative to the case with Minkowski bulk. We extend our study to the ease that induced curvature on the brahe is modified in the spirit of the f（R）-gravity.     

Tachyon Cosmology with Gauss–Bonnet and Non-Minimal Kinetic Couplings

We consider a tachyonic model of dark energy in which scalar field non-minimally coupled with curvature and kinetic part of its Lagrangian density.Additionally the model contains the Gauss–Bonnet coupling to the scalar field through an arbitrary function.The non-minimal Gauss–Bonnet coupling function and scalar field potential have been obtained for power-law solution and then for a dynamically varying equation of state.We have extracted the required condition for the so-called phantom divide line crossing in the model and represented such a crossing numerically.     

Holographic Dark Energy in Induced Gravity

Many astrophysics data show that our universe has a critical energy density, and 73% of it is dark energy, which drives the accelerating expansion of the universe. We consider the holographic dark energy in induced gravity by taking the Hubble scale, particle horizon and event horizon as the infrared cutoff. We find that only the event horizon can give accelerating expansion of our universe.     

Fluctuation with dust of de Sitter ground state of scalar-tensor gravity

An exact de Sitter solution of scalar-tensor gravity is found in our recent work, in which the non-minimal coupling scalar is rolling along a non-constant potential. Based on this solution, a dust-filled FRW universe is explored in frame of scalar-tensor gravity in this article. The effective dark energy induced by the sole non-minimal scalar can be quintessence-like, phantom-like, and more significantly, can cross the phantom divide. The rich and varied properties of scalar-tensor gravity even with only one scalar is shown.     

Localization of Gravity in Brane World with Arbitrary Extra Dimensions

We study the induced 4-dimensional linearized Einstein field equations in an m-dimensional bulk space by means of a confining potential. We used the confining potential in this model to localized gravitons on the brane. It is shown that in this approach the mass of graviton is quantized. The cosmological constant problem is also addressed within the context of this approach. We show that the difference between the values of the cosmological constant in particle physics and cosmology stems from our measurements in two different scales, small and large.     

Effective Gravity in Randall–Sundrum Infinite Brane World

The gravity induced on the brane in the Randall–Sundrum (RS) infinite brane world is briefly reviewed. We also discuss the possibility of the absence of black hole configuration in this model based on the argument of the AdS/CFT correspondence.     

Moduli Stabilization in Warped Compactifications at One Loop

We review the moduli stabilization mechanism found in Garriga et al. (Garriga, J., Pujolas, O., and Tanaka, T. (2000). Preprint hep-th/0111277.) for a class of five-dimensional warped brane-world scenarios. Specifically, we consider solutions with a power-law warp factor and a bulk dilaton with logarithmic profile in terms of the proper distance in the extra dimension. This includes the Heterotic M-theory brane-world of Lukas et al. (Lukas, A., Ovrut, B. A., Stelle, K. S., and Waldram, D. (1999). Physical Review D 59, 086001.) and Khoury et al. (Khoury, J., Ovrut, B. A., Steinhardt, P. J., and Turok, N. (2001). Preprint hep-th/0103239.) and the Randall–Sundrum (RS) model as a limiting case. In general, there are two moduli fields y _±, corresponding to the positions of two branes. Classically, the moduli are massless due to a scaling symmetry of the action. However, in the absence of supersymmetry, they develop an effective potential at one loop. Local terms proportional to some powers of the local curvature scale at the location of the corresponding brane are needed in order to remove the divergences in the effective potential. Such terms break the scaling symmetry and therefore act as stabilizers for the moduli. Moreover, for q 10, the observed hierarchy can be naturally generated by this potential, and the lightest modulus mass is of order m _– TeV.     

Cosmology in Massive Gravity

We argue that more cosmological solutions in massive gravity can be obtained if the metric tensor and the tensor Σμν defined by Stückelberg fields take the homogeneous and isotropic form.The standard cosmology with matter and radiation dominations in the past can be recovered and ΛCDM model is easily obtained.The dynamical evolution of the universe is modified at very early times.     

Modified holographic dark energy in DGP brane world

In this Letter, the cosmological dynamics of a modified holographic dark energy which is derived from the UV/IR duality by considering the black hole mass in higher dimensions as UV cutoff, is investigated in Dvali–Gabadadze–Porrati (DGP) brane world model. We choose Hubble horizon and future event horizon as IR cutoff respectively. And the two branches of the DGP model are both taken into account. When Hubble horizon is considered as IR cutoff, the modified holographic dark energy (HDE) behaves like an effect dark energy that modification of gravity in pure DGP brane world model acts and it can drive the expansion of the universe speed up at late time in ?=−1$?=-1$ branch which in pure DGP model cannot undergo an accelerating phase. When future event horizon acts as IR cutoff, the equation of state parameter of the modified HDE can cross the phantom divide.     

Brane Cosmology, Varying Speed of Light and Inflation in Models with One or More Extra Dimensions

We summarize the approach to brane cosmology known as mirage cosmology and use it to determine the Friedmann equation on a 3-brane embedded in different bulk spacetimes all with one or more extra dimensions. Usually, when there is more than one extra dimension the junction conditions, central to the usual brane world scenarios, are difficult to apply. This problem does not arise in mirage cosmology because the brane is treated as a test particle in the background spacetime. We discuss in detail the dynamics of a brane embedded in two specific 10D bulk spacetimes, namely Sch-AdS₅ × S₅ and a rotating black hole, and from the dynamics—which are now rather more complicated since the brane can move in all the extra dimensions—determine the new dark fluid terms in the brane Friedmann equation. Some of these, such as the cosmological constant term, are seen to be bulk dependent. We then show explicitly how this mirage cosmology approach matches with the familiar junction condition approach when there is just one extra dimension. The issue of a varying speed of light in mirage cosmology is addressed and we find a scenario in which c _eff always increases, tending asymptotically to c ₀ as the universe expands. Finally some comments are made regarding brane inflation and limitations of the mirage cosmology approach are also discussed.     

Modified Gravity with ln R Terms and Cosmic Acceleration

The modified gravity with ln R or R ^–n (ln R) ^m terms which grow at small curvature is discussed. It is shown that such a model which has a well-defined Newtonian limit may eliminate the need for dark energy and may provide the current cosmic acceleration. It is demonstrated that R ² terms are important not only for early time inflation but also to avoid the instabilities and the linear growth of the gravitational force. It is very interesting that the condition of no linear growth for gravitational force coincides with the one for scalar mass in the equivalent scalar-tensor theory to be very large. Thus, modified gravity with R ² term seems to be a viable classical theory.     

Letter: Palatini Formulation of Modified Gravity with Squared Scalar Curvature

In this paper we show that in the Palatini formulation of modified gravity, a R ² term cannot lead to an early time inflation, in opposite to the well-known conclusion when considering this model in the metric formulation.