arXiv subjects

Jianbo Lu

Publications and source records attributed to Jianbo Lu.

69 records · Page 4Linked to original sources

arXiv2010

Cosmological constraints on generalized Chaplygin gas model: Markov Chain Monte Carlo approach

We use the Markov Chain Monte Carlo method to investigate a global constraints on the generalized Chaplygin gas (GCG) model as the unification of dark matter and dark energy from the latest observational data: the Constitution dataset of type supernovae Ia (SNIa), the observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. In a non-flat universe, the constraint results for GCG model are, $Ω_{b}h^{2}=0.0235^{+0.0021}_{-0.0018}$ ($1σ$) $^{+0.0028}_{-0.0022}$ $(2σ)$, $Ω_{k}=0.0035^{+0.0172}_{-0.0182}$ ($1σ$) $^{+0.0226}_{-0.0204}$ $(2σ)$, $A_{s}=0.753^{+0.037}_{-0.035}$ ($1σ$) $^{+0.045}_{-0.044}$ $(2σ)$, $α=0.043^{+0.102}_{-0.106}$ ($1σ$) $^{+0.134}_{-0.117}$ $(2σ)$, and $H_{0}=70.00^{+3.25}_{-2.92}$ ($1σ$) $^{+3.77}_{-3.67}$ $(2σ)$, which is more stringent than the previous results for constraint on GCG model parameters. Furthermore, according to the information criterion, it seems that the current observations much support $Λ$CDM model relative to the GCG model.

astro-ph.CO↗

arXiv2010

Reconstructing Dark Energy Potentials From Parameterized Deceleration Parameters

In this paper, the properties of dark energy are investigated according to the parameterized deceleration parameter $q(z)$, which is used to describe the extent of the accelerating expansion of the universe. The potential of dark energy $V(ϕ)$ and the cosmological parameters, such as the dimensionless energy density $Ω_ϕ$, $Ω_{m}$, and the state parameter $w_ϕ$, are connected to it. Concretely, by giving two kinds of parameterized deceleration parameters $q(z)=a+\frac{bz}{1+z}$ and $q(z)=1/2+\frac{az+b}{(1+z)^2}$, the evolution of these parameters and the reconstructed potentials $V(ϕ)$ are plotted and analyzed. It's found that the potentials run away with the evolution of universe.

astro-ph.CO↗

arXiv2010

The Integrated Sachs-Wolfe Effect in Time Varying Vacuum Model

The integrated Sachs-Wolfe (ISW) effect is an important implication for dark energy. In this paper, we have calculated the power spectrum of the ISW effect in the time varying vacuum cosmological model, where the model parameter $β=4.407$ is obtained by the observational constraint of the growth rate. It's found that the source of the ISW effect is not only affected by the different evolutions of the Hubble function $H(a)$ and the dimensionless matter density $Ω_m(a)$, but also by the different growth function $D_+(a)$, all of which are changed due to the presence of matter production term in the time varying vacuum model. However, the difference of the ISW effect in $Λ(t)\textmd{CDM}$ model and $Λ\textmd{CDM}$ model is lessened to a certain extent due to the integration from the time of last scattering to the present. It's implied that the observations of the galaxies with high redshift are required to distinguish the two models.

astro-ph.CO↗

arXiv2010

Observational constraint on generalized Chaplygin gas model

We investigate observational constraints on the generalized Chaplygin gas (GCG) model as the unification of dark matter and dark energy from the latest observational data: the Union SNe Ia data, the observational Hubble data, the SDSS baryon acoustic peak and the five-year WMAP shift parameter. It is obtained that the best fit values of the GCG model parameters with their confidence level are $A_{s}=0.73^{+0.06}_{-0.06}$ ($1σ$) $^{+0.09}_{-0.09}$ $(2σ)$, $α=-0.09^{+0.15}_{-0.12}$ ($1σ$) $^{+0.26}_{-0.19}$ $(2σ)$. Furthermore in this model, we can see that the evolution of equation of state (EOS) for dark energy is similar to quiessence, and its current best-fit value is $w_{0de}=-0.96$ with the $1σ$ confidence level $-0.91\geq w_{0de}\geq-1.00$.

astro-ph.CO↗

arXiv2010

Geometrical Diagnostics for Generalized Chaplygin Gas

A new diagnostic method, $Om$ is applied to generalized Chaplygin gas (GCG) model as the unification of dark matter and dark energy. On the basis of the recently observed data: the Union supernovae, the observational Hubble data, the SDSS baryon acoustic peak and the five-year WMAP shift parameter, we show the discriminations between GCG and $Λ$CDM model. Furthermore, it is calculated that the current equation of state of dark energy $w_{0de}=-0.964$ according to GCG model.

astro-ph↗

arXiv2010

Area spectrum of near-extremal SdS black holes via the new interpretation of quasinormal modes

Motivated by the recent work about a new physical interpretation of quasinormal modes by Maggiore, we investigate the quantization of near-extremal Schwarzschild-de Sitter black holes in the four dimensional spacetime. Following Kunstatter's method, we derive the area and entropy spectrum of near-extremal Schwarzschild-de Sitter black holes which differs from Setare's result. Furthermore, we find that the derived a universal area spectrum is $2πn$ which is equally spaced.

astro-ph.CO↗

arXiv2010

Observational constraints on holographic dark energy with varying gravitational constant

We use observational data from Type Ia Supernovae (SN), Baryon Acoustic Oscillations (BAO), Cosmic Microwave Background (CMB) and observational Hubble data (OHD), and the Markov Chain Monte Carlo (MCMC) method, to constrain the cosmological scenario of holographic dark energy with varying gravitational constant. We consider both flat and non-flat background geometry, and we present the corresponding constraints and contour-plots of the model parameters. We conclude that the scenario is compatible with observations. In 1$σ$ we find $Ω_{\Lambda0}=0.72^{+0.03}_{-0.03}$, $Ω_{k0}=-0.0013^{+0.0130}_{-0.0040}$, $c=0.80^{+0.19}_{-0.14}$ and $Δ_G\equiv G'/G=-0.0025^{+0.0080}_{-0.0050}$, while for the present value of the dark energy equation-of-state parameter we obtain $w_0=-1.04^{+0.15}_{-0.20}$.

astro-ph.CO↗

arXiv2009

Cosmic Constraint on Ricci Dark Energy Model

In this paper, a holographic dark energy model, dubbed Ricci dark energy, is confronted with cosmological observational data from type Ia supernovae (SN Ia), baryon acoustic oscillations (BAO) and cosmic microwave background (CMB). By using maximum likelihood method, it is found out that Ricci dark energy model is a viable candidate of dark energy model with the best fit parameters: $Ω_{m0}=0.34\pm 0.04$, $α=0.38\pm 0.03$ with $1σ$ error. Here, $α$ is a dimensionless parameter related with Ricci dark energy $ρ_{R}$ and Ricci scalar $R$, i.e., $ρ_{R}\propto αR$.

astro-ph↗

arXiv2009

Generalized Holographic and Ricci Dark Energy Models

In this paper, we consider generalized holographic and Ricci dark energy models where the energy densities are given as $ρ_{R}=3c^2M^{2}_{pl}Rf(H^2/R)$ and $ρ_{h}=3c^2M^{2}_{pl}H^2g(R/H^2)$ respectively, here $f(x),g(y)$ are positive defined functions of dimensionless variables $H^2/R$ or $R/H^2$. It is interesting that holographic and Ricci dark energy densities are recovered or recovered interchangeably when the function $f(x)=g(y)\equiv 1$ or$f=g\equiv Id$ is taken respectively (for example $f(x),g(x)=1-ε(1-x)$, $ε=0 \text{or} 1$ respectively). Also, when $f(x)\equiv xg(1/x)$ is taken, the Ricci and holographic dark energy models are equivalents to a generalized one. When the simple forms $f(x)=1-ε(1-x)$ and $g(y)=1-η(1-y)$ are taken as examples, by using current cosmic observational data, generalized dark energy models are researched. As expected, in these cases, the results show that they are equivalent ($ε=1-η=1.312$) and Ricci-like dark energy is more favored relative to the holographic one where the Hubble horizon was taken as an IR cut-off. And, the suggestive combination of holographic and Ricci dark energy components would be $1.312 R-0.312H^2$ which is $2.312H^2+1.312\dot{H}$ in terms of $H^2$ and $\dot{H}$.

astro-ph.CO↗

arXiv2009

Time Variable Cosmological Constants from the Age of Universe

In this paper, time variable cosmological constant, dubbed {\it age cosmological constant}, is investigated motivated by the fact: any cosmological length scale and time scale can introduce a cosmological constant or vacuum energy density into Einstein's theory. The age cosmological constant takes the form $ρ_Λ=3c^2M^2_P/t_Λ^2$, where $t_Λ$ is the age of our universe or conformal time. The effective equation of state of age cosmological constant are $w^{eff}_Λ=-1+{2/3}\frac{\sqrt{Ω_Λ}}{c}$ and $w^{eff}_Λ=-1+{2/3}\frac{\sqrt{Ω_Λ}}{c}(1+z)$ when the age of universe and conformal time are taken as the role of cosmological time scales respectively. They are the same as the so-called agegraphic dark energy models. However, the evolution history are different from the agegraphic ones for their different evolution equations.

astro-ph.CO↗

arXiv2009

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↗

arXiv2009

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↗

arXiv2009

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↗

arXiv2008

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↗

arXiv2008

The Influence of Free Quintessence on Gravitational Frequency Shift and Deflection of Light with 4D momentum

Based on the 4D momentum, the influence of quintessence on the gravitational frequency shift and the deflection of light are examined in modified Schwarzschild space. We find that the frequency of photon depends on the state parameter of quintessence $w_q$: the frequency increases for $-1<w_q<-1/3$ and decreases for $-1/3<w_q<0$. Meanwhile, we adopt an integral power number $a$ ($a = 3ω_q + 2$) to solve the orbital equation of photon. The photon's potentials become higher with the decrease of $ω_q$. The behavior of bending light depends on the state parameter $ω_q$ sensitively. In particular, for the case of $ω_q = -1$, there is no influence on the deflection of light by quintessence. Else, according to the H-masers of GP-A redshift experiment and the long-baseline interferometry, the constraints on the quintessence field in Solar system are presented here.

gr-qc↗