A Single Model of Interacting Dark Energy: Generalized Phantom Energy or Generalized Chaplygin Gas

I present a model in which dark energy interacts with matter. The former is represented by a variable equation of state. It is shown that the phantom crossing takes place at zero redshift, moreover, stable scaling solution of the Friedmann equations is obtained. I show that dark energy is most probably be either generalized phantom energy or the generalized Chaplygin gas, while phantom energy is ruled out as a dark energy candidate.     

Evolution of Holographic Dark Energy in Interacting Modified Chaplygin Gas Model

We investigate the modified Chaplygin gas （MCG） with interaction between holographic dark energy proposed by Li and dark matter. In this model, evolution of the universe is described in detail, which is from deceleration to acceleration. Specifically, the evolutions of related cosmological quantities such as density parameter, the equation of state of holographic dark energy, deceleration parameter and transition redshift are discussed. Moreover, we also give their present values which are consistent with the lately observations. Furthermore, the results given by us show such a model can accommodate a transition of the dark energy from a normal state wx 〉 -1 to ωx 〈 -1 phantom regimes.     

Thermodynamical Aspects of Modified Holographic Dark Energy Model

We investigate the unified first law and the generalized second law in a modified holographic dark energy model. The thermodynamical analysis on the apparent horizon can work and the corresponding entropy formula is extracted from the systematic algorithm. The entropy correction term depends on the extra-dimension number of the brane as expected, but the interplay between the correction term and the extra dimensions is more complicated. With the unified first law of thermodynamics well-founded, the generalized second law of thermodynamics is discussed and it is found that the second law can be violated in certain circumstances. Particularly, if the number of the extra dimensions is larger than one, the generalized law of thermodynamics is always satisfied; otherwise, the validity of the second law can only be guaranteed with the Hubble radius greatly smaller than the crossover scale rcof the 5-dimensional DGP model.     

Thermodynamical Aspects of Modified Holographic Dark Energy Model

We investigate the unified first law and the generalized second law in a modified holographic dark energy model. The thermodynamical analysis on the apparent horizon can work and the corresponding entropy formula is extracted from the systematic algorithm. The entropy correction term depends on the extra-dimension number of the brane as expected, but the interplay between the correction term and the extra dimensions is more complicated. With the unified first law of thermodynamics well-founded, the generalized second law of thermodynamics is discussed and it is found that the second law can be violated in certain circumstances. Particularly, if the number of the extra dimensions is larger than one, the generalized law of thermodynamics is always satisfied; otherwise, the validity of the second law can only be guaranteed with the Hubble radius greatly smaller than the crossover scale r_c of the 5-dimensional DGP model.     

Generalized Chaplygin Gas Model as a New Agegraphic Dark Energy in Non-flat Universe

In this paper we consider a correspondence between the new agegraphic dark energy density and generalized Chaplygin gas energy density in non-flat FRW universe. Then we reconstruct the potential and the dynamics of the scalar field which describe the generalized Chaplygin cosmology.     

Role of Modified Chaplygin Gas as an Unified Dark Matter-Dark Energy Model in Collapsing Spherically Symmetric Dust Cloud

In this work gravitational collapse of a spherical dust cloud in the background of unified dark matter-dark energy model in the form of modified Chaplygin gas is studied. It is found that invisible matter (dark matter-dark energy) alone in the form of modified Chaplygin gas forms black hole. Also when both components of the fluid are present then the collapse favours the formation of black hole in cases the invisible matter dominates over ordinary dust. The conclusion is totally opposite to the usually known results.     

Rip Singularity Scenario and Bouncing Universe in a Chaplygin Gas Dark Energy Model

We choose a modified Chaplygin Gas Dark energy model for considering some its cosmological behaviors. In this regards, we study different Rip singularity scenarios and bouncing model of the universe in context of this model. We show that by using suitable parameters can explain some cosmological aspects of the model.     

Anisotropic Inflationary Scenario Via Generalized Chaplygin Gas Model

We investigate generalized chaplygin gas for warm inflationary scenario in the context of locally rotationally symmetric Bianchi type I universe model.We assume two different cases of dissipative coefficient,i.e.,constant as well as function of scalar field.We construct dynamical equations as well as a relationship between scalar and radiation energy densities under slow-roll approximation.We also derive slow-roll parameters,scalar and tensor power spectra,scalar spectral index,tensor to scalar ratio for analyzing inflationary background during high dissipative regime.We also use the WMAP7 data for the discussion of our parameters.     

Interacting New Generalized Chaplygin Gas

I present a model in which dark energy interacts with matter. The former is represented by a variable equation of state. It is shown that the phantom crossing takes place at zero redshift, moreover, stable scaling solution of the Friedmann equations is obtained. I show that dark energy is most probably be either generalized phantom energy or the generalized Chaplygin gas, while phantom energy is ruled out as a dark energy candidate.     

Statefinder Description in Generalized Holographic and Ricci Dark Energy Models

We have considered the generalized holographic and generalized Ricci dark energy models for acceleration of the universe. If the universe filled with only GHDE/GRDE the corresponding deceleration parameter, EOS parameter and statefinder parameters have been calculated. Next we have considered that the mixture of GHDE/GRDE and dark matter in interacting and non-interacting situations. Also the mixture of GHDE/GRDE and generalized Chaplygin gas have been analyzed during evolution of the universe. The natures of above mentioned parameters have been investigated for interacting and non-interacting situations. Finally, it follows that the prescribed models derive the acceleration of the universe.     

Letter: Gravitational Waves in the Generalized Chaplygin Gas Model

The consequences of taking the generalized Chaplygin gas as the dark energy constituent of the Universe on the gravitational waves are studied and the spectrum obtained from this model, for the flat case, is analyzed. Besides its importance for the study of the primordial Universe, the gravitational waves represent an additional perspective (besides the CMB temperature and polarization anisotropies) to evaluate the consistence of the different dark energy models and establish better constraints to their parameters. The analysis presented here takes this fact into consideration to open one more perspective of verification of the generalized Chaplygin gas model applicability. Nine particular cases are compared: one where no dark energy is present; two that simulate the -CDM model; two where the gas acts like the traditional Chaplygin gas; and four where the dark energy is the generalized Chaplygin gas. The different spectra permit to distinguish the -CDM and the Chaplygin gas scenarios.     

Evolution of Variable Generalized Chaplygin Gas

We consider the variable Generalized Chaplygin gas （VGCG） proposal for unification of dark matter and dark energy with p = pdc and ρ= pdm ＋ ρdc. The equation of state of the VGCG is given by p = -A0a^-n/ρ^α, where a is the scale factor. Some cosmological quantities such as the fractional contributions of different components of the universe Ωi （i respectively denotes baryons, dark matter and dark energy） to the critical density, the deceleration parameter q are all obtained. The transition from deceleration to acceleration is described in this model. In addition, we find the behaviour of variable Generalized Chaplgin gas is similar to dust-like matter at early times and will be quiessence or phantom at late stage.     

Constraining the Parameters of New Variable Modified Chaplygin Gas Model

Assuming the flat FRW universe in Einstein’s gravity filled with New Variable Modified Chaplygin gas (NVMCG) dark energy and dark matter having negligible pressure. In this research work we analyze the viability on the basis of recent observation. Hubble parameter H is expressed in terms of the observable parameters H ₀, $\varOmega_{m}^{0}$ and the model parameters A ₀, B ₀, C ₀, m, n, α and the red shift parameter z. Here we find a best fitted parameter range of A ₀, B ₀ keeping 0≤α≤1 and using Stern data set (12 points) by minimizing the χ ² test at 66 %, 90 % and 99 % confidence levels. Next we do the joint analysis with BAO and CMB observations. Again evaluating the distance modulus μ(z) vs redshift (z) curve obtained in the model NVMCG with dark matter with the best fitted value of the parameters and comparing with that derived from the Union2 compilation data.     

A Modified Dark Energy Model and Quintessence

The observational data indicate that about 70 % of the total energy density of the current state universe has been occupied by Dark Energy. This is said to be the cause of the accelerated expansion of universe. In this letter we shall use a curvature constant as a scalar field in the quintessence Dark Energy model, for an isotropic universe. Connected to the so-called model, we will specify a definite dynamical field equation from the initial action of the theory.     

Co-Existence of Modified Chaplygin Gas and Other Dark Energies in the Framework of Fractal Universe

In this work, we consider a non-flat universe in the framework of fractal cosmology. We have investigated the co-existence of different kinds of dark energy models such as tachyonic field, DBI-essence, hessence, k-essence, dilaton, quintessence with the modified Chaplygin gas (MCG) in fractal universe and obtained the statefinder parameters. The natures of the scalar fields and the concerned potentials have been analyzed by the correspondence scenario in the fractal universe.     

Dynamical Stability and Attractor of the Variable Generalized Chaplygin Gas Model

For the variable generalized Chaplygin gas （VGCG） as a dynamical system, its stability is analyzed and the related dynamical attractors are investigated. By analysis it is shown that there are two critical points corresponding to the matter-dominated phase and the VGCG dark energy-dominated phase, respectively. Moreover, when the parameters n, a and γ take some fixed values, the phase with ωVGCG = --0.92 is a dynamical attractor and the equation of state of VGCG reaches it from either ωVGCG 〉 --1 or ωVGCG 〈 --1, independent of the initial values of the dynamical system. This shows a satisfactory cosmological model： the early matter-dominated era, followed by the dark energy-dominated era. Meanwhile, the evolutions of density parameters Ωγ and ΩVGCG are quite different from each other. For different initial values of x and y, Ωγ decreases and ωVGCG increases as the time grows, they will eventually approach Ωγ = 0 and ωVGCG ---- 1. Furthermore, since different values of n or a may lead to different equation-of-state parameters ωVGCG, we also discuss the constraints on the parameters n and by the observation data.     

FRW Cosmological Model with Modified Chaplygin Gas and Dynamical System

The Friedmann-Robertson-Walker (FRW) model with dynamical Dark Energy (DE) in the form of modified Chaplygin gas (MCG) has been investigated. The evolution equations are reduced to an autonomous system on the two dimensional phase plane and it can be interpreted as the motion of the particle in an one dimensional potential. Also the dynamical system analysis has been extended to examine the critical points at infinity with will exist provided the equation of state parameter $\omega<-\frac{1}{3}$ . Finally, theoretical points are asymptotically stable or unstable.     

Dynamical Attractor of Modified Chaplygin Gas

The dynamical attractor of the modified Chaplygin gas （MCG） model is studied. The dynamical analysis indicates that the phase ωMCG = -1 is a dynamical attractor and the equation of state of the MCG approaches it from either ωMCG 〉 -1 or ωMCG 〈 -1, independent of the choice of its initial density parameter and the ratio of pressure to critical energy density. Therefore our universe will not end up with Big Rip in the future. Moreover, the evolutions of the density parameters Ωγ and ΩMCG are quite different. For different initial values of x and y, Ωγ decreases and ΩMCG increases as time increases, and they will eventually approach Ωe = 0 and ΩMCG = 1, i.e., de Sitter phase. This implies that when there is not the interaction （i.e., the energy transfer） between the barotropic background fluid and modified Chaplygin gas （MCG）, the behaviour of the MCG will be similar to ACDM in the future.     

Dynamical Evolution of Modified Chaplygin Gas

Based our previous work [Mod. Phys. Lett. A 22 （2007） 783, Gen. Relat. Gray. 39 （2007） 653], some properties of modified Chaplygin gas （MCG） as a dark energy model continue to be studied mainly in two aspects： one is the change rates of the energy density and energy transfer, and the other is the evolution of the growth index. It is pointed that the density of dark energy undergoes the change from decrease to increase no matter whether the interaction between dark energy and dark matter exists or not, but the corresponding transformation points are different from each other.Eurthermore, it is stressed that the MCG model even supports the existence of interaction between dark energy and dark matter, and the energy of transfer flows from dark energy to dark matter. The evolution of the interaction term with an ansatz 3Hc^2ρ is discussed with the MCG model. Moreover, the evolution of the growth index f in the MCG model without interaction is illustrated, from which we find that the evolutionary trajectory of f overlaps with that of the ACDM model when a 〉 0.7 and its theoretical value f ≈ 0.566 given by us at z = 0.15 is consistent with the observations.     

Statefinder Diagnostic in Generalized Chaplygin Gas Model with and Without Viscosity

Statefinder diagnostic is a useful method which can distinguish one dark energy model from the others. In this paper, we apply this method to the GCG model with and without viscosity. It is shown that the evolving trajectory of the viscous GCG model in the s–r diagram is not only quite different from the model without viscosity but also different from other dark energy models.