arXiv subjects

Jianbo Lu

Publications and source records attributed to Jianbo Lu.

At least 55 records · Page 3Linked to original sources

arXiv2016

A Poincare-Starobinsky-Yang-Mills type model of dark energy

Starting from the Poincare Gauge principle and a Starobinsky-Yang-Mills type Lagrangian a model of dark energy is developed. In order to evade any unnecessary controversy regarding frames (i.e. Einstein .vs. Jordan) the theory is treated using the original variables instead of transforming them to a scalar-tensor theory. The field equations are derived directly from the original Lagrangian using the variational principle. The cosmological equations are different from the Friedmann equations, but the acceleration equation gives the same result as the one of the $Λ$CDM model in the matter-dominated era. Furthermore, it indicates an inflation in the early time and the radiation-dominated era as the Starobinsky model. The cosmological constant naturally emerges from the Yang-Mills terms of the Lagrangian rather than be added artificially. The equation of state of the dark energy depends on the density of the matter and then the coincidence and fine tuning problem is solved naturally. In order to compare with the popular $Λ$CDM model, the cosmological perturbations is investigated. The equations for linear perturbations of the metric and for the density contrast growth are derived. The explicit analytic solutions are obtained. The gravitational potential and the growth of the baryon matter density perturbation can be used to clarify whether this model is in agreement with standard $Λ$CDM predictions and experimental data.

gr-qc↗

arXiv2015

Cosmic constraint on the unified model of dark sectors with or without a cosmic string fluid in the varying gravitational constant theory

Observations indicate that most of the universal matter are invisible and the gravitational constant $G(t)$ maybe depends on the time. A theory of the variational $G$ (VG) is explored in this paper, with naturally producing the useful dark components in universe. We utilize the observational data: lookback time data, model-independent gamma ray bursts, growth function of matter linear perturbations, type Ia supernovae data with systematic errors, CMB and BAO to restrict the unified model (UM) of dark components in VG theory. Using the best-fit values of parameters with the covariance matrix, constraints on the variation of $G$ are $(\frac{G}{G_{0}})_{z=3.5}\simeq 1.0015^{+0.0071}_{-0.0075}$ and $(\frac{\dot{G}}{G})_{today}\simeq -0.7252^{+2.3645}_{-2.3645}\times 10^{-13} yr^{-1}$, the small uncertainties around constants. Limit on the equation of state of dark matter is $w_{0dm}=0.0072^{+0.0170}_{-0.0170}$ with assuming $w_{0de}=-1$ in unified model, and dark energy is $w_{0de}=-0.9986^{+0.0011}_{-0.0011}$ with assuming $w_{0dm}=0$ at prior. Restriction on UM parameters are $B_{s}=0.7442^{+0.0137+0.0262}_{-0.0132-0.0292}$ and $α=0.0002^{+0.0206+0.0441}_{-0.0209-0.0422}$ with $1σ$ and $2σ$ confidence level. In addition, the effect of a cosmic string fluid on unified model in VG theory are investigated. In this case it is found that the $Λ$CDM ($Ω_{s}=0$, $β=0$ and $α=0$) is included in this VG-UM model at $1σ$ confidence level, and the larger errors are given: $Ω_{s}=-0.0106^{+0.0312+0.0582}_{-0.0305-0.0509}$ (dimensionless energy density of cosmic string), $(\frac{G}{G_{0}})_{z=3.5}\simeq 1.0008^{+0.0620}_{-0.0584}$ and $(\frac{\dot{G}}{G})_{today}\simeq -0.3496^{+26.3135}_{-26.3135}\times 10^{-13}yr^{-1}$.

astro-ph.CO↗

arXiv2015

Reduced modified Chaplygin gas cosmology

In this paper, we study cosmologies containing the reduced modified Chaplygin gas (RMCG) fluid which is reduced from the modified Chaplygin gas $p=Aρ-Bρ^{-α}$ for the value of $α=-1/2$. In this special case, dark cosmological models can be realized for different values of model parameter $A$. We investigate the viabilities of these dark cosmological models by discussing the evolutions of cosmological quantities and using the currently available cosmic observations. It is shown that the special RMCG model ($A=0$ or $A=1$) which unifies the dark matter and dark energy should be abandoned. For $A=1/3$, RMCG which unifies the dark energy and dark radiation is the favorite model according to the objective Akaike information criteria. In the case of $A<0$, RMCG can achieve the features of the dynamical quintessence and phantom models, where the evolution of the universe is not sensitive to the variation of model parameters.

astro-ph.CO↗

arXiv2013

Self-gravitational Interaction in z = 4 Horava-Lifshitz Gravity

Motivated by recent works [1,2], the influences of self-gravitational interaction on the Hawking radiation are studied both for (3 + 1) and (4 + 1) dimensional black holes in $z = 4$ Hourava-Lifshitz gravity. It is found that the tunneling entropies $S_{B(3 + 1)}$ and $S_{B(4 + 1)}$ independent on particle's mass are consistent with the thermodynamical entropies $S_{BH(3 + 1)}$ and $S_{BH(4 + 1)}$, respectively. There is a very visible degree of uniformity between thermodynamics and quantum tunneling in $z = 4$ Hourava-Lifshitz gravity. It suggests that the entropies contained corrected terms could be explained well by the self-gravitational interaction of Hawking radiation. The study of tunneling process may shed light on understanding the Hourava-Lifshitz gravity.

gr-qc↗

arXiv2012

Spectrums of Black Hole in de Sitter Spacetime with Highly Damped Quasinormal Modes: High Overtone Case

Motivated by recent physical interpretation on quasinormal modes presented by Maggiore, the adiabatic quantity method given by Kunstatter is used to calculate the spectrums of a non-extremal Schwarzschild de Sitter black hole in this paper, as well as electrically charged case. According to highly damped Konoplya and Zhidenko's numerical observational results for high overtone modes\cite{Konoplya}, we found that the asymptotic non-flat spacetime structure leads two interesting facts as followings: (i) near inner event horizon, the area and entropy spectrums, which are given by $A_{en} = 8 n_1 π\hbar$, $S_{en} = 2πn_1\hbar$, are equally spaced accurately. (ii) However, near outer cosmological horizon the spectrums, which are in the form of $A_{cn} = 16 n_2 π\hbar - \sqrt{\frac{48π}ΛA_{cn} - 3 A_{cn}^2}$, $S_{cn} = 4 πn_2 \hbar - \sqrt{\frac{3π}ΛA_{cn} - 3/16 A_{cn}^2}$, are not markedly equidistant. Finally, we also discuss the electrically charged case and find the black holes in de Sitter spacetime have similar quantization behavior no matter with or without charge.

gr-qc↗

arXiv2012

Revisiting Generalized Chaplygin Gas as a Unified Dark Matter and Dark Energy Model

In this paper, we revisit generalized Chaplygin gas (GCG) model as a unified dark matter and dark energy model. The energy density of GCG model is given as $ρ_{GCG}/ρ_{GCG0}=[B_{s}+(1-B_{s})a^{-3(1+α)}]^{1/(1+α)}$, where $α$ and $B_s$ are two model parameters which will be constrained by type Ia supernova as standard candles, baryon acoustic oscillation as standard rulers and the seventh year full WMAP data points. In this paper, we will not separate GCG into dark matter and dark energy parts any more as adopted in the literatures. By using Markov Chain Monte Carlo method, we find the result: $α=0.00126_{- 0.00126- 0.00126}^{+ 0.000970+ 0.00268}$ and $B_s= 0.775_{- 0.0161- 0.0338}^{+ 0.0161+ 0.0307}$.

astro-ph.CO↗

arXiv2012

Modified f(G) gravity models with curvature-matter coupling

A modified f(G) gravity model with coupling between matter and geometry is proposed, which is described by the product of the Lagrange density of the matter and an arbitrary function of the Gauss-Bonnet term. The field equations and the equations of motion corresponding to this model show the non-conservation of the energy-momentum tensor, the presence of an extra-force acting on test particles and the non-geodesic motion. Moreover, the energy conditions and the stability criterion at de Sitter point in the modified f(G) gravity models with curvature-matter coupling are derived, which can degenerate to the well-known energy conditions in general relativity. Furthermore, in order to get some insight on the meaning of these energy conditions, we apply them to the specific models of f(G) gravity and the corresponding constraints on the models are given. In addition, the conditions and the candidate for late-time cosmic accelerated expansion in the modified f(G) gravity are studied by means of conditions of power-law expansion and the equation of state of matter less than -1/ 3 .

astro-ph.CO↗

arXiv2012

Investigate the interaction between dark matter and dark energy

In this paper we investigate the interaction between dark matter and dark energy by considering two different interacting scenarios, i.e. the cases of constant interaction function and variable interaction function. By fitting the current observational data to constrain the interacting models, it is found that the interacting strength is non-vanishing, but weak for the case of constant interaction function, and the interaction is not obvious for the case of variable interaction function. In addition, for seeing the influence from interaction we also investigate the evolutions of interaction function, effective state parameter for dark energy and energy density of dark matter. At last some geometrical quantities in the interacting scenarios are discussed.

astro-ph.CO↗

arXiv2012

Cosmological constraints on the generalized holographic dark energy

We use the Markov ChainMonte Carlo method to investigate global constraints on the generalized holographic (GH) dark energy with flat and non-flat universe from the current observed data: the Union2 dataset of type supernovae Ia (SNIa), high-redshift Gamma-Ray Bursts (GRBs), the observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. The most stringent constraints on the GH model parameter are obtained. In addition, it is found that the equation of state for this generalized holographic dark energy can cross over the phantom boundary wde =-1.

astro-ph.CO↗

arXiv2012

Time variable cosmological constant of holographic origin with interaction in Brans-Dicke theory

Time variable cosmological constant (TVCC) of holographic origin with interaction in Brans-Dicke theory is discussed in this paper. We investigate some characters for this model, and show the evolutions of deceleration parameter and equation of state (EOS) for dark energy. It is shown that in this scenario an accelerating universe can be obtained and the evolution of EOS for dark energy can cross over the boundary of phantom divide. In addition, a geometrical diagnostic method, jerk parameter is applied to this model to distinguish it with cosmological constant.

astro-ph.CO↗

arXiv2011

Does accelerating universe indicates Brans-Dicke theory

The evolution of universe in Brans-Dicke (BD) theory is discussed in this paper. Considering a parameterized scenario for BD scalar field $ϕ=ϕ_{0}a^α$ which plays the role of gravitational "constant" $G$, we apply the Markov Chain Monte Carlo method to investigate a global constraints on BD theory with a self-interacting potential according to the current observational data: Union2 dataset of type supernovae Ia (SNIa), high-redshift Gamma-Ray Bursts (GRBs) data, observational Hubble data (OHD), the cluster X-ray gas mass fraction, the baryon acoustic oscillation (BAO), and the cosmic microwave background (CMB) data. It is shown that an expanded universe from deceleration to acceleration is given in this theory, and the constraint results of dimensionless matter density $Ω_{0m}$ and parameter $α$ are, $Ω_{0m}=0.286^{+0.037+0.050}_{-0.039-0.047}$ and $α=0.0046^{+0.0149+0.0171}_{-0.0171-0.0206}$ which is consistent with the result of current experiment exploration, $\midα\mid \leq 0.132124$. In addition, we use the geometrical diagnostic method, jerk parameter $j$, to distinguish the BD theory and cosmological constant model in Einstein's theory of general relativity.

astro-ph.CO↗

arXiv2011

Fermions Analysis of IR modified Horava-Lifshitz gravity: Tunneling and Perturbation Perspectives

In this paper, we investigate the fermions Hawking radiation and quasinormal modes in infra-red modified Ho$\check{r}$ava-Lifshitz gravity under tunneling and perturbation perspectives.Firstly, through the fermions tunneling in IR modified Ho$\check{r}$ava-Lifshitz gravity,we obtain the Hawking radiation emission rate, tunneling temperature and entropy for the Kehagias-Sfetsos black hole. It is found that the results of fermions tunneling are in consistence with the thermodynamics results obtained by calculating surface gravity.Secondly, we numerically calculate the lowing quasinormal modes frequencies of fermions perturbations by using WKB formulas including the third orders and the sixth orders approximations simultaneously. It turns out that the actual frequency of fermions perturbation is larger than in the Schwarzschild case, and the damping rate is smaller than for the pure Schwarzschild. The resluts of fermions perturbation suggest the quasinormal modes could be lived more longer in Ho$\check{r}$ava-Lifshitz gravity.

hep-th↗

arXiv2011

Combined constraints on modified Chaplygin gas model from cosmological observed data: Markov Chain Monte Carlo approach

We use the Markov Chain Monte Carlo method to investigate a global constraints on the modified Chaplygin gas (MCG) model as the unification of dark matter and dark energy from the latest observational data: the Union2 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 flat universe, the constraint results for MCG model are, $Ω_{b}h^{2}=0.02263^{+0.00184}_{-0.00162}$ ($1σ$) $^{+0.00213}_{-0.00195}$ $(2σ)$, $B_{s}=0.7788^{+0.0736}_{-0.0723}$ ($1σ$) $^{+0.0918}_{-0.0904}$ $(2σ)$, $α=0.1079^{+0.3397}_{-0.2539}$ ($1σ$) $^{+0.4678}_{-0.2911}$ $(2σ)$, $B=0.00189^{+0.00583}_{-0.00756}$ ($1σ$) $^{+0.00660}_{-0.00915}$ $(2σ)$, and $H_{0}=70.711^{+4.188}_{-3.142}$ ($1σ$) $^{+5.281}_{-4.149}$ $(2σ)$.

astro-ph.CO↗

arXiv2011

Constraints on kinematic models from the latest observational data

Kinematical models are constrained by the latest observational data from geometry-distance measurements, which include 557 type Ia supernovae (SNIa) Union2 data and 15 observational Hubble data. Considering two parameterized deceleration parameter, the values of current deceleration parameter $q_{0}$, jerk parameter $j_{0}$ and transition redshift $z_{T}$, are obtained. Furthermore, we show the departures for two parameterized kinematical models from $Λ$CDM model according to the evolutions of jerk parameter $j(z)$. Also, it is shown that the constraint on jerk parameter $j(z)$ is weak by the current geometrical observed data.

astro-ph.CO↗

arXiv2010

Solar system constraints on asymptotically flat IR modified Horava gravity through light deflection

In this paper, we study the motion of photons around a Kehagias-Sfetsos (KS) black hole and obtain constraints on IR modified Ho$\check{r}$ava gravity without cosmological constant ($\sim Λ_{W}$). An analytic formula for the light deflection angle is obtained. For a propagating photon, the deflection angle $δϕ$ increases with large values of the Ho$\check{r}$ava gravity parameter $ω$. Under the UV limit $ω\longrightarrow \infty$, deflection angle reduces to the result of usual Schwarzschild case, $4GM/R$. It is also found that with increasing scale of astronomical observation system the Ho$\check{r}$ava-Lifshitz gravity should satisfy $|ωM^2|>1.1725 \times10^{-16}$ with 12% precision for Earth system, $|ωM^2| > 8.27649 \times 10^{-17}$ with 17% precision for Jupiter system and $|ωM^2| > 8.27650\times 10^{-15}$ with 0.17% precision for solar system.

gr-qc↗

arXiv2010

Time Variable Cosmological Constants from Cosmological Horizons

In this paper, motivated from the fact that a de Sitter cosmological boundary corresponds to a positive cosmological constant, we consider time variable cosmological constants, dubbed {\it horizon cosmological constants}. The horizon cosmological constants correspond to Hubble horizon, future event horizon and particle horizon are discussed respectively. When the Hubble horizon is taken as a cosmological length scale, the effective equation of state of horizon cosmological constant is quintessence-like. The values of model parameter $c$ will determine the current status of our universe. When particle horizon is taken as the cosmological length scale, non viable cosmological model can be obtained for the requirement of $Ω_Λ<1/3$ which conflicts with current comic observations. When the future event horizon is taken as the role of cosmological length scale, the forms of effective equation of state of horizon cosmological constants are the the same as the holographic ones. But, their evolutions are different because of the effective interaction with cold dark matter.

astro-ph.CO↗

arXiv2010

A more general interacting model of holographic dark energy

So far, there have been no theories or observational data that deny the presence of interaction between dark energy and dark matter. We extend naturally the holographic dark energy (HDE) model, proposed by Granda and Oliveros, in which the dark energy density includes not only the square of the Hubble scale, but also the time derivative of the Hubble scale to the case with interaction and the analytic forms for the cosmic parameters are obtained under the specific boundary conditions. The various behaviors concerning the cosmic expansion depend on the introduced numerical parameters which are also constrained. The more general interacting model inherits the features of the previous ones of HDE, keeping the consistency of the theory.

astro-ph.CO↗

arXiv2010

Constraints on modified Chaplygin gas from recent observations and a comparison of its status with other models

In this Letter, a modified Chaplygin gas (MCG) model of unifying dark energy and dark matter with the exotic equation of state $p_{MCG}=Bρ_{MCG} -\frac A{ρ_{MCG}^α}$ is constrained from recently observed data: the 182 Gold SNe Ia, the 3-year WMAP and the SDSS baryon acoustic peak. It is shown that the best fit value of the three parameters ($B$,$B_{s}$,$α$) in MCG model are (-0.085,0.822,1.724). Furthermore, we find the best fit $w(z)$ crosses -1 in the past and the present best fit value $w(0)=-1.114<-1$, and the $1σ$ confidence level of $w(0)$ is $-0.946\leq w(0)\leq-1.282$. Finally, we find that the MCG model has the smallest $χ^{2}_{min}$ value in all eight given models. According to the Alaike Information Criterion (AIC) of model selection, we conclude that recent observational data support the MCG model as well as other popular models.

astro-ph.CO↗