Searcharxiv⌕ Search

arXiv subjects

Lixin Xu

Publications and source records attributed to Lixin Xu.

At least 145 records · Page 8Linked to original sources

Constraints on Kinematic Model from Recent Cosmic Observations: SN Ia, BAO and Observational Hubble Data

In this paper, linear first order expansion of deceleration parameter $q(z)=q_0+q_1(1-a)$ ($M_1$), constant jerk $j=j_0$ ($M_2$) and third order expansion of luminosity distance ($M_3$) are confronted with cosmic observations: SCP 307 SN Ia, BAO and observational Hubble data (OHD). Likelihood is implemented to find the best fit model parameters. All these models give the same prediction of the evolution of the universe which is undergoing accelerated expansion currently and experiences a transition from decelerated expansion to accelerated expansion. But, the transition redshift depends on the concrete parameterized form of the model assumed. $M_1$ and $M_2$ give value of transition redshift about $z_t\sim 0.6$. $M_3$ gives a larger one, say $z_t\sim 1$. The $χ^2/dof$ implies almost the same goodness of the models. But, for its badness of evolution of deceleration parameter at high redshift $z>1$, $M_3$ can not be reliable. $M_1$ and $M_2$ are compatible with $Λ$CDM model at the $2σ$ and $1σ$ confidence levels respectively. $M_3$ is not compatible with $Λ$CDM model at $2σ$ confidence level. From $M_1$ and $M_2$ models, one can conclude that the cosmic data favor a cosmological model having $j_0<-1$.

astro-ph.CO↗

Cosmic Constraints on Holographic Dark Energy in Brans-Dicke Theory

In this paper, the holographic dark energy in Brans-Dicke theory is confronted by cosmic observations from SN Ia, BAO and CMB shift parameter. The best fit parameters are found in $1σ$ region: $Ω_{h0}=0.683^{+0.035}_{-0.038}$, $c=0.605^{+0.138}_{-0.107}$ and $α=0.00662^{+0.00477}_{-0.00467}$ (equivalently $ω=905.690^{+637.906}_{-651.471}$ which is less the solar system bound and consistent with other constraint results). With these best fit values of the parameters, it is found the universe is undergoing accelerated expansion, and the current value of equation of state of holographic dark energy $w_{h0}=-1.246^{+0.191}_{-0.144}$ which is phantom like in Brans-Dicke theory. The evolution of effective Newton's constant is also explored.

astro-ph.CO↗

Holographic Dark Energy in Brans-Dicke Theory

In this paper, the holographic dark energy model is considered in Brans-Dicke theory where the holographic dark energy density $ρ_Λ =3c^2 M^{2}_{pl} L^{-2}$ is replaced with $ρ_{h}=3c^2 Φ(t)L^{-2}$. Here $Φ(t)=\frac{1}{8πG}$ is a time variable Newton constant. With this replacement, it is found that no accelerated expansion universe will be achieved when the Hubble horizon is taken as the role of IR cut-off. When the event horizon is adopted as the IR cut-off, an accelerated expansion universe is obtained. In this case, the equation of state of holographic dark energy $w_h$ takes a modified form $w_h=-{1/3}(1+α+\frac{2}{c}\sqrt{Ω_{h}})$. In the limit $α\to 0$, the 'standard' holographic dark energy is recovered. In the holographic dark energy dominated epoch, power-law and de Sitter time-space solutions are obtained.

astro-ph↗

Constraints on accelerating universe using ESSENCE and Gold supernovae data combined with other cosmological probes

We use recently observed data: the 192 ESSENCE type Ia supernovae (SNe Ia), the 182 Gold SNe Ia, the 3-year WMAP, the SDSS baryon acoustic peak, the X-ray gas mass fraction in clusters and the observational $H(z)$ data to constrain models of the accelerating universe. Combining the 192 ESSENCE data with the observational $H(z)$ data to constrain a parameterized deceleration parameter, we obtain the best fit values of transition redshift and current deceleration parameter $z_{T}=0.632^{+0.256}_{-0.127}$, $q_{0}=-0.788^{+0.182}_{-0.182}$. Furthermore, using $Λ$CDM model and two model-independent equation of state of dark energy, we find that the combined constraint from the 192 ESSENCE data and other four cosmological observations gives smaller values of $Ω_{0m}$ and $q_{0}$, but a larger value of $z_{T}$ than the combined constraint from the 182 Gold data with other four observations. Finally, according to the Akaike information criterion it is shown that the recently observed data equally supports three dark energy models: $Λ$CDM, $w_{de}(z)=w_{0}$ and $w_{de}(z)=w_{0}+w_{1}\ln(1+z)$.

astro-ph↗

Using Energy Conditions to Distinguish Brane Models and Study Brane Matter

Current universe (assumed here to be normal matter on the brane) is pressureless from observations. In this case the energy condition is $ρ_0\geq0$ and $p_0=0$. By using this condition, brane models can be distinguished. Then, assuming arbitrary component of matter in DGP model, we use four known energy conditions to study the matter on the brane. If there is nonnormal matter or energy (for example dark energy with $w<-1/3$) on the brane, the universe is accelerated.

gr-qc↗

$5D$ Solutions to $Λ$CDM Universe Derived from Global Brane Model

An exact solution of brane universe is studied and the result indicates that Friedmann equations on the brane are modified with an extra term. This term can play the role of dark energy and make the universe accelerate. In order to derive the $Λ$CDM Universe from this global brane model, the new solutions are obtained to describe the $5D$ manifold.

hep-th↗

Power-law cosmological solution derived from DGP brane with a brane tachyon field

By studying a tachyon field on the DGP brane model, in order to embed the 4D standard Friedmann equation with a brane tachyon field in 5D bulk, the metric of the 5D spacetime is presented. Then, adopting the inverse square potential of tachyon field, we obtain an expanding universe with power-law on the brane and an exact 5D solution.

hep-th↗

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↗

Correspondence Between DGP Brane Cosmology and 5D Ricci-flat Cosmology

We discuss the correspondence between the DGP brane cosmology and 5D Ricci-flat cosmology by letting their metrics equal each other. By this correspondence, a specific geometrical property of the arbitrary integral constant I in DGP metric is given and it is related to the curvature of 5D bulk. At the same time, the relation of arbitrary functions $μ$ and $ν$ in a class of Ricci-flat solutions is obtained from DGP brane metric.

gr-qc↗

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↗

The Real Solution to Scalar Field Equation in 5D Black String Space

After the nontrivial quantum parameters $Ω_{n}$ and quantum potentials $V_{n}$ obtained in our previous research, the circumstance of a real scalar wave in the bulk is studied with the similar method of Brevik (2001). The equation of a massless scalar field is solved numerically under the boundary conditions near the inner horizon $r_{e}$ and the outer horizon $r_{c}$. Unlike the usual wave function $Ψ_{ωl}$ in 4D, quantum number $n$ introduces a new functions $Ψ_{ωl n}$, whose potentials are higher and wider with bigger n. Using the tangent approximation, a full boundary value problem about the Schr$\ddot{o}$dinger-like equation is solved. With a convenient replacement of the 5D continuous potential by square barrier, the reflection and transmission coefficients are obtained. If extra dimension does exist and is visible at the neighborhood of black holes, the unique wave function $Ψ_{ωl n}$ may say something to it.

gr-qc↗

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↗

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↗

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↗

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↗

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↗

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↗

Radiation and Potential Barriers of a 5D Black String Solution

By using a massless scalar field we examine the effect of an extra dimension on black hole radiation. Because the equations are coupled, we find that the structure of the fifth dimension (as for membrane and induced-matter theory) affects the nature of the radiation observed in four-dimensional spacetime. In the case of the Schwarzschild-de Sitter solution embedded in a Randall-Sundrum brane model, the extension of the black hole along the fifth dimension looks like a black string. Then it is shown that, on the brane, the potential barrier surrounding the black hole has a quantized as well as a continuous spectrum. In principle, Hawking radiation may thus provide a probe for higher dimensions.

gr-qc↗