arXiv subjects

Z. G. Huang

Publications and source records attributed to Z. G. Huang.

15 recordsLinked to original sources

arXiv2010

$Om$ Diagnostic for Dilaton Dark Energy

$Om$ diagnostic can differentiate between different models of dark energy without the accurate current value of matter density. We apply this geometric diagnostic to dilaton dark energy(DDE) model and differentiate DDE model from LCDM. We also investigate the influence of coupled parameter $α$ on the evolutive behavior of $Om$ with respect to redshift $z$. According to the numerical result of $Om$, we get the current value of equation of state $ω_{\sigma0}$=-0.952 which fits the WMAP5+BAO+SN very well.

astro-ph.CO↗

arXiv2009

Parametrization of Born-Infeld Type Phantom Dark Energy Model

Applying the parametrization of dark energy density, we can construct directly independent-model potentials. In Born-Infeld type phantom dark energy model, we consider four special parametrization equation of state parameter. The evolutive behavior of dark energy density with respect to red-shift $z$, potentials with respect to $ϕ$ and $z$ are shown mathematically. Moreover, we investigate the effect of parameter $η$ upon the evolution of the constructed potential with respect to $z$. These results show that the evolutive behavior of constructed Born-Infeld type dark energy model is quite different from those of the other models.

hep-th↗

arXiv2008

Statefinder Diagnostic for Dilaton Dark Energy

Statefinder diagnostic is a useful method which can differ one dark energy model from the others. The Statefinder pair $\{r, s\}$ is algebraically related to the equation of state of dark energy and its first time derivative. We apply in this paper this method to the dilaton dark energy model based on Weyl-Scaled induced gravitational theory. We investigate the effect of the coupling between matter and dilaton when the potential of dilaton field is taken as the Mexican hat form. We find that the evolving trajectory of our model in the $r-s$ diagram is quite different from those of other dark energy models.

hep-th↗

arXiv2008

The Consistent Result of Cosmological Constant From Quantum Cosmology and Inflation with Born-Infeld Scalar Field

The Quantum cosmology with Born-Infeld(B-I) type scalar field is considered. In the extreme limits of small cosmological scale factor the wave function of the universe can also be obtained by applying the methods developed by Hartle-Hawking(H-H) and Vilenkin. H-H wave function predicts that most Probable cosmological constant $Λ$ equals to $\frac{1}η$($\frac{1}{2η}$ equals to the maximum of the kinetic energy of scalar field). It is different from the original results($Λ=0$) in cosmological constant obtained by Hartle-Hawking. The Vilenkin wave function predicts a nucleating unverse with largest possible cosmological constant and it is larger than $1/η$. The conclusions have been nicely to reconcile with cosmic inflation. We investigate the inflation model with B-I type scalar field, and find that $η$ depends on the amplitude of tensor perturbation $δ_h$, with the form $\frac{1}η\simeq \frac{m^2}{12π[(\frac{9δ_Φ^2}{N δ_h^2})^2-1]}.$ The vacuum energy in inflation epoch depends on the tensor-to-scalar ratio $\frac{δ_h}{δ_Φ}$. The amplitude of the tensor perturbation ${δ_{h}}$ can, in principle, be large enough to be discovered. However, it is only on the border of detectability in future experiments. If it has been observed in future, this is very interesting to determine the vacuum energy in inflation epoch.

hep-th↗

arXiv2008

Statefinder Diagnostic for Born-Infeld Type Dark Energy Model

Using a new method--statefinder diagnostic which can differ one dark energy model from the others, we investigate in this letter the dynamics of Born-Infeld(B-I) type dark energy model. The evolutive trajectory of B-I type dark energy with Mexican hat potential model with respect to $e-folding$ time $N$ is shown in the $r(s)$ diagram. When the parameter of noncanonical kinetic energy term $η\to0$ or kinetic energy $\dotϕ^2\to0$, B-I type dark energy(K-essence) model reduces to Quintessence model or $Λ$CDM model corresponding to the statefinder pair $\{r, s\}$=$\{1, 0\}$ respectively. As a result, the the evolutive trajectory of our model in the $r(s)$ diagram in Mexican hat potential is quite different from those of other dark energy models.

hep-th↗

arXiv2007

Potentials of Coupled Quintessence Based on a Dilaton

In this paper, we regard dilaton in Weyl-scaled induced gravitational theory as coupled Quintessence, which is called DCQ model by us. Parametrization of the dark energy model is a good method by which we can construct the scalar potential directly from the effective equation of state function $ω_σ(z)$ describing the properties of the dark energy. Applying this method to the DCQ model, we consider four parametrizations of $ω(z)$ and investigate the features of the constructed DCQ potentials, which possess two different evolutive behaviors called "O" mode and "E" mode. Lastly, we comprise the results of the constructed DCQ model with those of quintessence model numerically.

hep-th↗

arXiv2007

Exponential Potentials and Attractor Solution of Dilatonic Cosmology

We present the scalar-tensor gravitational theory with an exponential potential in which pauli metric is regarded as the physical space-time metric. We show that it is essentially equivalent to coupled quintessence(CQ) model. However for baryotropic fluid being radiation there are in fact no coupling between dilatonic scalar field and radiation. We present the critical points for baryotropic fluid and investigate the properties of critical points when the baryotropic matter is specified to ordinary matter. It is possible for all the critical points to be attractors as long as the parameters $λ$ and $β$ satisfy certain conditions. To demonstrate the attractor behaviors of these critical points, We numerically plot the phase plane for each critical point. Finally with the bound on $β$ from the observation and the fact that our universe is undergoing an accelerating expansion, we conclude that present accelerating expansion is not the eventual stage of universe. Moreover, we numerically describe the evolution of the density parameters $Ω$ and the decelerating factor $q$, and computer the present values of some cosmological parameters, which are consistent with current observational data.

hep-th↗

arXiv2007

Cosmology in Nonlinear Born-Infeld Scalar Field Theory With Negative Potentials

The cosmological evolution in Nonlinear Born-Infeld(hereafter NLBI) scalar field theory with negative potentials was investigated. The cosmological solutions in some important evolutive epoches were obtained. The different evolutional behaviors between NLBI and linear(canonical) scalar field theory have been presented. A notable characteristic is that NLBI scalar field behaves as ordinary matter nearly the singularity while the linear scalar field behaves as "stiff" matter. We find that in order to accommodate current observational accelerating expanding universe the value of potential parameters $|m|$ and $|V_0|$ must have an {\it upper bound}. We compare different cosmological evolutions for different potential parameters $m, V_0$.

hep-th↗

arXiv2007

Cosmologies with General Non-Canonical Scalar Field

We generally investigate the scalar field model with the lagrangian $L=F(X)-V(ϕ)$, which we call it {\it General Non-Canonical Scalar Field Model}. We find that it is a special square potential(with a negative minimum) that drives the linear field solution($ϕ=ϕ_0t$) while in K-essence model(with the lagrangian $L=-V(ϕ)F(X)$) the potential should be taken as an inverse square form. Hence their cosmological evolution are totally different. We further find that this linear field solutions are highly degenerate, and their cosmological evolutions are actually equivalent to the divergent model where its sound speed diverges. We also study the stability of the linear field solution. With a simple form of $F(X)=1-\sqrt{1-2X}$ we indicate that our model may be considered as a unified model of dark matter and dark energy. Finally we study the case when the baryotropic index $γ$ is constant. It shows that, unlike the K-essence, the detailed form of F(X) depends on the potential $V(ϕ)$. We analyze the stability of this constant $γ_0$ solution and find that they are stable for $γ_0\leq1$. Finally we simply consider the constant c_s^2 case and get an exact solution for F(X)

hep-th↗

arXiv2006

Born-Infeld Type Phantom Model in the $ω-ω'$ Plane

In this paper, we investigate the dynamics of Born-Infeld(B-I) phantom model in the $ω-ω'$ plane, which is defined by the equation of state parameter for the dark energy and its derivative with respect to $N$(the logarithm of the scale factor $a$). We find the scalar field equation of motion in $ω-ω'$ plane, and show mathematically the property of attractor solutions which correspond to $ω_ϕ\sim-1$, $Ω_ϕ=1$, which avoid the "Big rip" problem and meets the current observations well.

hep-th↗

arXiv2006

Dilaton Coupled Quintessence Model in the $ω-ω'$ Plane

In this paper, we regard dilaton in Weyl-scaled induced gravitational theory as a coupled quintessence. Based on this consideration, we investigate the dilaton coupled quintessence(DCQ) model in $ω-ω'$ plane, which is defined by the equation of state parameter for the dark energy and its derivative with respect to $N$(the logarithm of the scale factor $a$). We find the scalar field equation of motion in $ω-ω'$ plane, and show mathematically the property of attractor solutions which correspond to $ω_σ\sim-1$, $Ω_σ=1$. Finally, we find that our model is a tracking one which belongs to "freezing" type model classified in $ω-ω'$ plane.

hep-th↗

arXiv2006

Coupled Quintessence and Phantom Based On a Dilaton

Based on dilatonic dark energy model, we consider two cases: dilaton field with positive kinetic energy(coupled quintessence) and with negative kinetic energy(phantom). In the two cases, we investigate the existence of attractor solutions which correspond to an equation of state parameter $ω=-1$ and a cosmic density parameter $Ω_σ=1$. We find that the coupled term between matter and dilaton can't affect the existence of attractor solutions. In the Mexican hat potential, the attractor behaviors, the evolution of state parameter $ω$ and cosmic density parameter $Ω$, are shown mathematically. Finally, we show the effect of coupling term on the evolution of $X(\fracσ{σ_0})$ and $Y(\frac{\dotσ}{σ^2_0})$ with respect to $N(lna)$ numerically.

hep-th↗

arXiv2005

Quantum Cosmology and Dark Energy Model of Born-Infeld Type Scalar Field

In this paper, we consider a quantum model of gravitation interacting with a Born-Infeld(B-I) type scalar field $ϕ$. The corresponding Wheeler-Dewitt equation can be solved analytically for both very large and small cosmological scale factor. In the condition that small cosmological scale factor tend to limit, the wave function of the universe can be obtained by applying the methods developed by Vilenkin, Hartle and Hawking. Both Vilenkin's and Hartle-Hawking's wave function predicts nonzero cosmological constant. The Vilenkin's wave function predicts a universe with a cosmological constant as large as possible, while the Hartle-Hawking's wave function predicts a universe with positive cosmological constant, which equals to $\frac{1}λ$. It is different from Coleman's result that cosmological constant is zero, and also different from Hawking's prediction of zero cosmological constant in quantum cosmology with linear scalar field. We suggest that dark energy in the universe might result from the B-I type scalar field with potential and the universe can undergo a phase of accelerating expansion. The equation of state parameter lies in the range of $-1<$w$<-{1/3}$. When the potential $V(ϕ)=\frac{1}λ$, our Lagrangian describes the Chaplygin gas. In order to give a explanation to the observational results of state parameter w$<-1$, we also investigate the phantom model that posses negative kinetic energy. We find that weak and strong energy conditions are violated for phantom B-I type scalar field. At last, we study a specific potential with the form $V_0(1+\fracϕ{ϕ_0})e^{-(\fracϕ{ϕ_0})}$ in phantom B-I scalar field in detail. The attractor property of the system is shown by numerical analysis.

hep-th↗

arXiv2005

The Evolution of Universe with th B-I Type Phantom Scalar Field

We considered the phantom cosmology with a lagrangian $\displaystyle L=\frac{1}η[1-\sqrt{1+ηg^{μν}ϕ_{, μ}ϕ_{, ν}}]-u(ϕ)$, which is original from the nonlinear Born-Infeld type scalar field with the lagrangian $\displaystyle L=\frac{1}η[1-\sqrt{1-ηg^{μν}ϕ_{, μ}ϕ_{, ν}}]-u(ϕ)$. This cosmological model can explain the accelerated expansion of the universe with the equation of state parameter $w\leq-1$. We get a sufficient condition for a arbitrary potential to admit a late time attractor solution: the value of potential $u(X_c)$ at the critical point $(X_c,0)$ should be maximum and large than zero. We study a specific potential with the form of $u(ϕ)=V_0(1+\fracϕ{ϕ_0})e^{(-\fracϕ{ϕ_0})}$ via phase plane analysis and compute the cosmological evolution by numerical analysis in detail. The result shows that the phantom field survive till today (to account for the observed late time accelerated expansion) without interfering with the nucleosynthesis of the standard model(the density parameter $Ω_ϕ\simeq10^{-12}$ at the equipartition epoch), and also avoid the future collapse of the universe.

hep-th↗

arXiv2004

Dark Energy and Dilaton Cosmology

We studied the dilaton cosmology based on Weyl-Scaled induced gravity. The potential of dilaton field is taken as exponential form. An analytical solution of Einstein equation is found. The dilaton can be a candidate for dark energy that can explain the accelerated universe. The structure formation is also considered. We find the the evolutive equation of density perturbation, and its growth is quicker than the one in standard model which is consistent with the constraint from CMBR measurements

hep-th↗