arXiv subjects

Chengwu Zhang

Publications and source records attributed to Chengwu Zhang.

10 recordsLinked to original sources

arXiv2007

Dark Energy in Global Brane Universe

We discuss the exact solutions of brane universes and the results indicate the Friedmann equations on the branes are modified with a new density term. Then, we assume the new term as the density of dark energy. Using Wetterich's parametrization equation of state (EOS) of dark energy, we obtain the new term varies with the red-shift z. Finally, the evolutions of the mass density parameter $Ω_2$, dark energy density parameter $Ω_x$ and deceleration parameter q_2 are studied.

gr-qc↗

arXiv2007

Reconstruction of 5D Cosmological Model From Recent Observations

We use a parameterized equation of state (EOS) of dark energy to a 5D Ricci-flat cosmological solution and suppose the universe contains two major components: dark matter and dark energy. Using the recent observational datasets: the latest 182 type Ia Supernovae Gold data, the 3-year WMAP CMB shift parameter and the SDSS baryon acoustic peak, we obtain the best fit values of the EOS and two major components' evolution. We find that the best fit EOS crossing -1 in the near past $z\simeq 0.07$, the present best fit value of $w_x(0)<-1$ and for this model the universe experiences the acceleration at about $z\simeq 0.5$.

astro-ph↗

arXiv2007

Statefinder Diagnostic for Phantom Model with $V(ϕ)=V_{0}\exp(-λϕ^2)$

We investigate the phantom field with potential $V(ϕ)=V_{0}\exp(-λϕ^2)$ and dark matter in the spatially flat FRW model. It has been shown by numerical calculation that there is a attractor solution in this model. We also apply the statefinder diagnostic to this phantom model. It is shown that the evolving trajectories of this scenario in the $s-r$ diagram is quite different form other dark energy models.

astro-ph↗

arXiv2007

Statefinder Parameters for Five-Dimensional Cosmology

We study the statefinder parameter in the five-dimensional big bounce model, and apply it to differentiate the attractor solutions of quintessence and phantom field. It is found that the evolving trajectories of these two attractor solutions in the statefinder parameters plane are quite different, and that are different from the statefinder trajectories of other dark energy models.

astro-ph↗

arXiv2007

Comparison of Supernovae datasets Constraints on Dark Energy

Cosmological measurements suggest that our universe contains a dark energy component. In order to study the dark energy evolution, we constrain a parameterized dark energy equation of state $w(z)=w_0 + w_1 \frac{z}{1+z}$ using the recent observational datasets: 157 Gold type Ia supernovae and the newly released 182 Gold type Ia supernovae by maximum likelihood method. It is found that the best fit $w(z)$ crosses -1 in the past and the present best fit value of $w(0)<-1$ obtained from 157 Gold type Ia supernovae. The crossing of -1 is not realized and $w_0=-1$ is not ruled out in $1σ$ confidence level for the 182 Gold type Ia supernovae. We also find that the range of parameter $w_0$ is wide even in $1σ$ confidence level and the best fit $w(z)$ is sensitive to the prior of $Ω_m$.

astro-ph↗

arXiv2007

Reconstruction of Deceleration Parameters from Recent Cosmic Observations

In this paper, three kinds of simple parameterized deceleration parameters $q(z)=a+\frac{b z}{1+z}$, $q(z)=a+\frac{b z}{(1+z)^2}$ and $q(z)={1/2}+\frac{a z+b}{(1+z)^2}$ are reconstructed from the latest Sne Ia Gold dataset, observational Hubble data and their combination. It is found that the transition redshift from decelerated expansion to accelerated expansion $z_T$ and current decelerated parameter values $q_0$ are consistent with each other in $1σ$ region by only using Sne Ia Gold dataset and observational Hubble data in three parameterizations respectively. By combining the Sne Ia Gold dataset and observational Hubble data together, a tight constraint is obtained. With this combined constraints, $z_T$ is $0.505^{+0.080}_{-0.052}$, $0.368^{+0.059}_{-0.036}$, $0.767^{+0.121}_{-0.126}$ with $1σ$ error in three parameterizations respectively. And, it is easy to see that $z_T$ separates from each other in $1σ$ region clearly.

astro-ph↗

arXiv2007

Statefinder Parameters for Interacting Phantom Energy with Dark Matter

We apply in this paper the statefinder parameters to the interacting phantom energy with dark matter. There are two kinds of scaling solutions in this model. It is found that the evolving trajectories of these two scaling solutions in the statefinder parameter plane are quite different, and that are also different from the statefinder diagnostic of other dark energy models.

astro-ph↗

arXiv2007

Reconstruction of a Deceleration Parameter from the Latest Type Ia Supernovae Gold Dataset

In this paper, a parameterized deceleration parameter $q(z)= 1/2 - a/(1 + z)^b$ is reconstructed from the latest type Ia supernovae gold dataset. It is found out that the transition redshift from decelerated expansion to accelerated expansion is at $z_T=0.35^{+0.14}_{-0.07}$ with $1σ$ confidence level in this parameterized deceleration parameter. And, the best fit values of parameters in $1σ$ errors are $a=1.56^{+0.99}_{-0.55}$ and $b=3.82^{+3.70}_{-2.27}$.

astro-ph↗

arXiv2006

Universe Evolution in a 5D Ricci-flat Cosmology

We use Wetterich's parameterization equation of state (EOS) of dark energy to a $5D$ Ricci-flat cosmological solution and we suppose the universe contains three major components: matter, radiation and dark energy. By using the relation between the scale factor and the redshift $z$, we show that the two arbitrary functions contained in the $5D$ solution could be solved out analytically in terms of the variable $z$. Thus the whole $5D$ solution could be constructed uniquely if the current values of the three density parameters $Ω_{m0}$, ${Ω_{r0}}$, $Ω_{x0}$, the EOS $w_{0}$%, and the bending parameter $b$ contained in the EOS are all known. Furthermore, we find that all the evolutions of the mass density $Ω_{m} $, the radiation density ${Ω_{r}}$, the dark energy density $Ω_{x}$, and the deceleration parameter $q$ depend on the bending parameter $b$ sensitively. Therefore it is deserved to study observational constraints on the bending parameter $b$.

astro-ph↗

arXiv2005

Reconstruction of $5D$ Cosmological Models From Equation of State of Dark Energy

We consider a class of five-dimensional cosmological solutions which contains two arbitrary function $μ(t)$ and $ν(t)$. We found that the arbitrary function $μ(t)$ contained in the solutions can be rewritten in terms of the redshift $z$ as a new arbitrary function $f(z)$. We further showed that this new arbitrary function $f(z)$ could be solved out for four known parameterized equations of state of dark energy. Then the $5D$ models can be reconstructed and the evolution of the density and deceleration parameters of the universe can be determined.

astro-ph↗