Ghost Dark Energy Research Articles

Interacting two-component fluid models with varying EoS parameter

In this paper, we consider Universe filled with two-component fluid. We study two different models. In the first model we assume barotropic fluid with the linear equation of state (EoS) as the first component of total fluid. In the second model we assume van der Waals gas as the first component of total fluid. In both models, the second component assumed generalized ghost dark energy. We consider also interaction between components and discuss, numerically, cosmological quantities for two different parametrizations of EoS which varies with time. We consider this as a toy model of our Universe. We fix parameters of the model by using generalized second law of thermodynamics. Comparing our results with some observational data suggests interacting barotropic fluid with EoS parameter [Formula: see text] and generalized ghost dark energy as an appropriate model to describe our Universe.

Interaction between modified Chaplygin gas and ghost dark energy in the presence of extra dimensions

In this paper, we consider three different models of dark energy in higher dimensional space-time and discuss about some cosmological parameters numerically. The first model is a single component universe including viscous varying modified Chaplygin gas. In the second model, we consider two-component universe including viscous varying modified Chaplygin gas and ghost dark energy. In the third model, we consider another two-component universe including viscous modified cosmic Chaplygin gas and ghost dark energy. In the cases of two-component fluids we also consider possibility of interaction between components.

Entropy and thermodynamics of ghost dark energy

We study the thermodynamics of the ghost model of dark energy in a flat Friedmann–Robertson–Walker (FRW) universe enveloped by a Hubble horizon. We show that the Friedmann equation of the FRW universe, in the presence of ghost dark energy, can be transformed to the first law of thermodynamics on the Hubble horizon. Using this procedure, we extract the entropy expression associated with the horizon in this model. We find that the area relation for the entropy expression is modified and an additional term that is proportional to the volume of the system, A3/2, appears in the entropy relation. We also find that for late time, where the temperature of the Universe scales as the temperature of its horizon, T = bTin, the generalized second law of thermodynamics can be secured provided 1/2 ≤ b ≤ 1, where T and Tin are the horizon and the matter fields’ temperatures, respectively.

Generalized second law of thermodynamics in QCD ghost f(G) gravity

Considering power-law for of scale factor in a flat FRW universe we reported a reconstruction scheme for f(G) gravity based on QCD ghost dark energy. We reconstructed the effective equation of state parameter and observed “quintessence” behavior of the equation of state parameter. Furthermore, considering dynamical apparent horizon as the enveloping horizon of the universe we have observed that the generalized second law of thermodynamics is valid for this reconstructed f(G) gravity.

Cosmological constraints on ghost dark energy in the Brans–Dicke theory by using MCMC approach

By using a Markov Chain Monte Carlo simulation, we investigate cosmological constraints on the ghost dark energy (GDE) model in the framework of the Brans–Dicke (BD) theory. A combination of the latest observational data of the cosmic microwave background radiation data from seven-year WMAP, the baryon acoustic oscillation data form the SDSS, the supernovae type Ia data from the Union2 and the X-ray gas mass fraction data from the Chandra X-ray observations of the largest relaxed galaxy clusters are used to perform constraints on GDE in the BD cosmology. In this paper, we consider both flat and non-flat universes together with interaction between dark matter and dark energy. The main cosmological parameters are obtained as: Ωbh2=0.0223−0.0013+0.0016, Ωch2=0.1149−0.0104+0.0088 and Ωk=0.0005−0.0073+0.0025. In addition, the Brans–Dicke parameter ω is estimated as 1/ω≃0.002.

QCD ghost reconstruction of f(T) gravity in flat FRW universe

The present paper reports a reconstruction scheme for f(T) gravity based on QCD ghost dark energy. Two models of f(T) have been generated and the pressure and density contributions due to torsion have been reconstructed. Two realistic models have been obtained and the effective equations of state have been studied. Also, the squared speed of sound has been studied to examine the stability of the models.

Reconstruction of ghost scalar fields

In the literature, a large number of approaches have been done to reconstruct the potential and dynamics of the scalar fields by establishing a connection between holographic/Ricci/new agegraphic/ghost energy density and a scalar field model of dark energy. In most of these attempts, the analytical form of the potentials in terms of the scalar field have not been reconstructed due to the complexity of the equations involved. In the present work, we establish a correspondence between ghost dark energy and quintessence, tachyon and dilaton scalar field models in anisotropic Bianchi type-I universe to reconstruct the dynamics of these scalar fields.

Ghost dark energy models in Bianchi I cosmologies with modified gravity

A ghost dark energy model has been recently put forward to explain the current accelerated expansion of the universe. In this model, we develop the general scheme for modified f(R) gravity reconstruction from realistic anisotropic Bianchi type I cosmology. Power-law volumetric expansion is used to obtain exact solutions of the field equations. We discuss the physical behavior of the solutions and anisotropy behavior of the fluid, the expansion parameter, and the model in future evolution of the universe. We reconstruct corresponding f(R) gravities and obtain the equation of state parameter. We show that the corresponding f(R) gravity of the ghost dark energy model can behave like phantom or quintessence of the selected models that describe accelerated expansion of the universe.

SCALAR FIELDS RECONSTRUCTION OF VISCOUS GDE WITH VARYING G

In this paper, we first study the effects of the varying gravitational constant G as well as the bulk viscosity on the evolution of the Universe field with pressureless dark matter and ghost dark energy (GDE). Then, we establish a correspondence between viscous GDE and scalar field models of dark energy including quintessence, tachyon, K-essence and dilaton energy density in a flat FRW universe. This correspondence allows us to reconstruct the potential and dynamics of the scalar fields according to the evolution of interacting viscous GDE with varying G.

QCD Ghost Dark Energy in RS II Braneworld with Bulk-Brane Interaction

We investigate the QCD ghost model of dark energy in the framework of RS II braneworld. We assume there is an energy flow between the brane and bulk, and hence the continuity equation for the ghost dark energy is violated, while it is still preserved for the dark matter on the brane. We find that with the brane-bulk interaction, the equation of state parameter of ghost dark energy on the brane, can cross the phantom line w D =−1 at the present time, which confirms by some cosmological evidences. This result is in contrast to the standard cosmology where w D of ghost dark energy never cross the phantom line and the universe enters a de Sitter phase at the late time.

COSMOGRAPHY OF INTERACTING GENERALIZED QCD GHOST DARK ENERGY

Exploring the accelerated expansion of the universe, we investigate the generalized ghost dark energy (GGDE) model from the statefinder diagnostic analysis in a flat Friedmann–Robertson–Walker universe. First, we calculate the cosmological evolution and statefinder trajectories for noninteracting case and then extend this work by considering the interaction between dark matter and dark energy components. We show that in the noninteracting case the phantom line cannot be crossed and also the evolutionary trajectories of model in s - r plane cannot be discriminated. It has been shown that the present location of model in s - r plane would be close to observational value for negative values of the model parameter. In the presence of interaction between dark matter and dark energy, the phantom regime is achieved, the accelerated phase of expansion occurs sooner compared with the noninteracting case. The GGDE model is also discussed from the viewpoint of perturbation theory by calculating the adiabatic sound speed of the model. Finally, unlike the noninteracting case, the evolutionary trajectories in s - r plane can be discriminated in the interacting model. Like the noninteracting model, in the interacting case the present location of GGDE model is closer to observational value for negative values of the model parameter.

Interacting ghost dark energy models with variable G and Λ

In this paper we consider several phenomenological models ofvariable Λ. Model of a flat Universe with variable Λand G is accepted. It is well known, that varying G andΛ gives rise to modified field equations and modifiedconservation laws, which gives rise to many different manipulationsand assumptions in literature. We will consider two component fluid,which parameters will enter to Λ. Interaction between fluidswith energy densities ρ1 and ρ2 assumed asQ = 3Hb(ρ1+ρ2). We have numerical analyze of importantcosmological parameters like EoS parameter of the composed fluid anddeceleration parameter q of the model.

Holographic, new agegraphic, and ghost dark energy models in fractal cosmology

We investigate the holographic, new agegraphic, and ghost dark energy models in the framework of fractal cosmology. We consider a fractal flat Friedmann–Robertson–Walker universe filled with dark energy and matter. We obtain the deceleration and equation of state parameters of the selected dark energy models in the ultraviolet regime and discuss their implications in the early universe.

QCD ghost f(T)-gravity model

Within the framework of modified teleparallel gravity, we reconstruct a f(T) model corresponding to the QCD ghost dark energy scenario. For a spatially flat FRW universe containing only the pressureless matter, we obtain the time evolution of the torsion scalar T (or the Hubble parameter). Then, we calculate the effective torsion equation of state parameter of the QCD ghost f(T)-gravity model as well as the deceleration parameter of the universe. Furthermore, we fit the model parameters by using the latest observational data including SNeIa, CMB and BAO data. We also check the viability of our model using a cosmographic analysis approach. Moreover, we investigate the validity of the generalized second law (GSL) of gravitational thermodynamics for our model. Finally, we point out the growth rate of matter density perturbation. We conclude that in QCD ghost f(T)-gravity model, the universe begins a matter dominated phase and approaches a de Sitter regime at late times, as expected. Also this model is consistent with current data, passes the cosmographic test, satisfies the GSL and fits the data of the growth factor well as the LCDM model.

Generalized Ghost Dark Energy Model with Varying G

The cosmological implications of the generalized ghost dark energy model in the presence of varying gravitational constant is investigated. In particular, evolution of the cosmological parameters such as the equation of state and the deceleration parameters are studied. The investigation is also generalized to the more general case where there is a bulk viscosity in the cosmic fluids. It is shown that by taking 0 < △G ≤ 0:07, = 0:01 and assuming Ω 0 = 0:73 for the present time, we find −0:80 < w 0 ≤ −0:78 and −0:41 < q0 ≤ −0:36 for the present ranges of the equation of state and the deceleration parameters. This values are consistent with the recent observations.

QCD ghost dark energy cannot (even roughly) explain the main features of the accepted cosmological paradigm

We explore the whole phase space of the so-called Veneziano/QCD ghost dark energy models where the dynamics of the inner trapping horizon is ignored and also the more realistic models where the time dependence of the horizon is taken into consideration. We pay special attention to the choice of phase space variables leading to bounded and compact phase space so that no critical point of physical interest is missing. It is demonstrated that ghost dark energy is not a suitable candidate to explain the presently accepted cosmological paradigm, since no critical point associated with matter dominance is found in the physical phase space of the model. A transient stage of matter dominance---responsible for the observed amount of cosmic structure---is an essential ingredient of the accepted cosmological paradigm. The above drawback is in addition to the well-known problem with classical instability against small perturbations of the background density originated from negativity of the sound speed squared.

Generalized ghost dark energy in Brans–Dicke theory

It was argued that the vacuum energy of the Veneziano ghost field of QCD, in a time-dependent background, can be written in the general form, H + O(H2), where H is the Hubble parameter. Based on this, a phenomenological dark energy model whose energy density is of the form ρ = αH + βH2 was recently proposed to explain the dark energy dominated universe. In this paper, we investigate this generalized ghost dark energy model in the setup of Brans–Dicke cosmology. We study the cosmological implications of this model. In particular, we obtain the equation of state, the deceleration parameters, and a differential equation governing the evolution of this dark energy model. It is shown that the equation of state parameter of the generalized ghost dark energy can cross the phantom line (wD = −1) in some range of the parameters spaces.

Sounds of Instability from Generalized QCD Ghost Dark Energy

We investigate about the stability of generalized QCD ghost dark energy model against perturbations in the FRW background. For this purpose, we use the squared sound speed $v_s^2$ whose sign determines the stability of the model. We explore the stability of this model in the presence/absence of interaction between dark energy and dark matter in both flat and non-flat geometry. In all cases we find almost a same result. Based on the square sound speed analysis, due to the existence of a free parameter in this model, the model is theoretically capable to lead a dark energy dominated stable universe. However, observational constraints rule out such a chance. In conclusion, we find evidences that the generalized ghost dark energy might can not lead to a stable universe favored by observations at the present time.

QCD MODIFIED GHOST SCALAR FIELD DARK ENERGY MODELS

Within the framework of FRW cosmology, we study the QCD modified ghost scalar field models of dark energy (DE) in the presence of both interaction and viscosity. For a spatially nonflat FRW universe containing modified ghost dark energy (MGDE) and dark matter (DM), we obtain the equation of state of MGDE, the deceleration parameter as well as a differential equation governing the MGDE density parameter. We also investigate the growth of structure formation for our model in a linear perturbation regime. Furthermore, we reconstruct both the dynamics and potentials of the quintessence, tachyon, K-essence and dilaton scalar field DE models according to the evolution of the MGDE density.

Interacting viscous ghost tachyon, K-essence and dilaton scalar field models of dark energy

We study the correspondence between the interacting viscous ghost dark energy model with the tachyon, K-essence and dilaton scalar field models in the framework of Einstein gravity. We consider a spatially non-flat FRW universe filled with interacting viscous ghost dark energy and dark matter. We reconstruct both the dynamics and potential of these scalar field models according to the evolutionary behavior of the interacting viscous ghost dark energy model, which can describe the accelerated expansion of the universe. Our numerical results show that the interaction and viscosity have opposite effects on the evolutionary properties of the ghost scalar field models.