arXiv subjects

Puxun Wu

Publications and source records attributed to Puxun Wu.

At least 109 records · Page 6Linked to original sources

arXiv2010

The growth factor of matter perturbations in an f(R) gravity

The growth of matter perturbations in the $f(R)$ model proposed by Starobinsky is studied in this paper. Three different parametric forms of the growth index are considered respectively and constraints on the model are obtained at both the $1σ$ and $2σ$ confidence levels, by using the current observational data for the growth factor. It is found, for all the three parametric forms of the growth index examined, that the Starobinsky model is consistent with the observations only at the $2σ$ confidence level.

gr-qc↗

arXiv2010

Probing the course of cosmic expansion with a combination of observational data

We study the cosmic expansion history by reconstructing the deceleration parameter $q(z)$ from the SDSS-II type Ia supernova sample (SNIa) with two different light curve fits (MLCS2k2 and SALT-II), the baryon acoustic oscillation (BAO) distance ratio, the cosmic microwave background (CMB) shift parameter, and the lookback time-redshift (LT) from the age of old passive galaxies. Three parametrization forms for the equation of state of dark energy (CPL, JBP, and UIS) are considered. Our results show that, for the CPL and the UIS forms, MLCS2k2 SDSS-II SNIa+BAO+CMB and MLCS2k2 SDSS-II SNIa+BAO+CMB+LT favor a currently slowing-down cosmic acceleration, but this does not occur for all other cases, where an increasing cosmic acceleration is still favored. Thus, the reconstructed evolutionary behaviors of dark energy and the course of the cosmic acceleration are highly dependent both on the light curve fitting method for the SNIa and the parametrization form for the equation of state of dark energy.

gr-qc↗

arXiv2010

Observational constraints on $f(T)$ theory

The $f(T)$ theory, which is an extension of teleparallel, or torsion scalar $T$, gravity, is recently proposed to explain the present cosmic accelerating expansion with no need of dark energy. In this Letter, we first perform the statefinder analysis and $Om(z)$ diagnostic to two concrete $f(T)$ models, i.e., $f(T)=α(-T)^n$ and $f(T)=-αT(1-e^{p {T_0}/T})$, and find that a crossing of phantom divide line is impossible for both models. This is contrary to an existing result where a crossing is claimed for the second model. We, then, study the constraints on them from the latest Union 2 Type Ia Supernova (Sne Ia) set, the baryonic acoustic oscillation (BAO), and the cosmic microwave background (CMB) radiation. Our results show that at the 95% confidence level $Ω_{m0}=0.272_{-0.032}^{+0.036}$, $n=0.04_{-0.33}^{+0.22}$ for Model 1 and $Ω_{m0}=0.272_{-0.034}^{+0.036}$, $p=-0.02_{-0.20}^{+0.31}$ for Model 2. A comparison of these two models with the $Λ$CDM by the $χ^2_{Min}/dof$ (dof: degree of freedom) criterion indicates that $Λ$CDM is still favored by observations. We also study the evolution of the equation of state for the effective dark energy in the theory and find that Sne Ia favors a phantom-like dark energy, while Sne Ia + BAO + CMB prefers a quintessence-like one.

gr-qc↗

arXiv2010

The dynamical behavior of $f(T)$ theory

Recently, a new model obtained from generalizing teleparallel gravity, named $f(T)$ theory, is proposed to explain the present cosmic accelerating expansion with no need of dark energy. In this paper, we analyze the dynamical property of this theory. For a concrete power law model, we obtain that the dynamical system has a stable de Sitter phase along with an unstable radiation dominated phase and an unstable matter dominated one. We show that the Universe can evolve from a radiation dominated era to a matter dominated one, and finally enter an exponential expansion phase.

astro-ph.CO↗

arXiv2010

Emergent universe from the Hořava-Lifshitz gravity

We study the stability of the Einstein static universe in the Hořava-Lifshitz (HL) gravity and a generalized version of it formulated by Sotiriou, Visser and Weifurtner. We find that, for the HL cosmology, there exists a stable Einstein static state if the cosmological constant $Λ$ is negative. The universe can stay at this stable state eternally and thus the big bang singularity can be avoided. However, in this case, the Universe can not exit to an inflationary era. For the Sotiriou, Visser and Weifurtner HL cosmology, if the cosmic scale factor satisfies certain conditions initially, the Universe can stay at the stable state past eternally and may undergo a series of infinite, nonsingular oscillations. Once the parameter of the equation of state $w$ approaches a critical value, the stable critical point coincides with the unstable one, and the Universe enters an inflationary era. Therefore, the big bang singularity can be avoided and a subsequent inflation can occur naturally.

gr-qc↗

arXiv2010

The stability of Einstein static universe in the DGP braneworld

The stability of an Einstein static universe in the DGP braneworld scenario is studied in this paper. Two separate branches denoted by $ε=\pm1$ of the DGP model are analyzed. Assuming the existence of a perfect fluid with a constant equation of state, $w$, in the universe, we find that, for the branch with $ε=1$, there is no a stable Einstein static solution, while, for the case with $ε=-1$, the Einstein static universe exists and it is stable when $-1<w<-1/3$. Thus, the universe can stay at this stable state past-eternally and may undergo a series of infinite, non-singular oscillations. Therefore, the big bang singularity problem in the standard cosmological model can be resolved.

gr-qc↗

arXiv2010

Constraints on Cosmological Models and Reconstructing the Acceleration History of the Universe with Gamma-Ray Burst Distance Indicators

Gamma-ray bursts (GRBs) have been regarded as standard candles at very high redshift for cosmology research. We have proposed a new method to calibrate GRB distance indicators with Type Ia supernova (SNe Ia) data in a completely cosmology-independent way to avoid the circularity problem that had limited the direct use of GRBs to probe cosmology [N. Liang, W. K. Xiao, Y. Liu, and S. N. Zhang, Astrophys. J. 685, 354 (2008).]. In this paper, a simple method is provided to combine GRB data into the joint observational data analysis to constrain cosmological models; in this method those SNe Ia data points used for calibrating the GRB data are not used to avoid any correlation between them. We find that the $Λ$CDM model is consistent with the joint data in the 1-$σ$ confidence region, using the GRB data at high redshift calibrated with the interpolating method, the Constitution set of SNe Ia, the cosmic microwave background radiation from Wilkinson Microwave Anisotropy Probe five year observation, the baryonic acoustic oscillation from the spectroscopic Sloan Digital Sky Survey Data Release 7 galaxy sample, the x-ray baryon mass fraction in clusters of galaxies, and the observational Hubble parameter versus redshift data. Comparing to the joint constraints with GRBs and without GRBs, we find that the contribution of GRBs to the joint cosmological constraints is a slight shift in the confidence regions of cosmological parameters to better enclose the $Λ$CDM model. Finally, we reconstruct the acceleration history of the Universe up to $z>6$ with the distance moduli of SNe Ia and GRBs and find some features that deviate from the $Λ$CDM model and seem to favor oscillatory cosmology models; however further investigations are needed to better understand the situation.

astro-ph.CO↗

arXiv2009

Testing the (generalized) Chaplygin gas model with the Lookback time-Redshift data

The Chaplygin gas (CG) and the generalized Chaplygin gas (GCG) models, proposed as candidates of the unified dark matter-dark energy (UDME), are tested with the look-back time (LT) redshift data. We find that the LT data only give a very weak constraint on the model parameter. However, by combing the LT with the baryonic acoustic oscillation peak, we obtain, at the 95.4% confidence level, $0.68\leq A_c\leq0.82$ and $0.59\leq h\leq0.65$ for the CG model, and $0.67\leq A_s\leq0.89$ and $-0.29\leq α\leq0.61$ for the GCG model. This shows that both the CG and the GCG are viable as a candidate of UDME. Within the GCG model, we also find that the Chaplygin gas model ($α=1$) is ruled out by these data at the 99.7% confidence level.

astro-ph.CO↗

arXiv2009

Latest Observational Constraints on Cardassian Models

Constraints on the original Cardassian model and the modified polytropic Cardassian model are examined from the latest derived 397 Type Ia supernova (SNe Ia) data, the size of baryonic acoustic oscillation peak from the Sloan Digital Sky Survey (SDSS), the position of first acoustic peak of the Cosmic Microwave Background radiation (CMB) from the five years Wilkinson Microwave Anisotropy Probe (WMAP), the x-ray gas mass fractions in clusters of galaxies, and the observational H(z) data. In the original Cardassian model with these combined data set, we find $Ω_{m0}=0.271^{+0.014}_{-0.014}, n=0.035^{+0.049}_{-0.049}$ at $1 σ$ confidence level. And in the modified polytropic Cardassian model, we find that $Ω_{m0}=0.271^{+0.014}_{-0.015}$, $n=-0.091^{+0.331}_{-1.908}$ and $β=0.824^{+0.750}_{-0.622}$ within $1σ$ confidence level. According to these observations, the acceleration of the universe begins at $z_T=0.55^{+0.05}_{-0.05} (1σ)$ for the original Cardassian model, and at $z_T=0.58^{+0.12}_{-0.12} (1σ)$ for the modified polytropic Cardassian model. Evolution of the effective equation of state $w_{eff}$ for the modified polytropic Cardassian model is also examined here and results show that an evolutionary quintessence dark energy model is favored.

astro-ph.CO↗

arXiv2009

A parametrization for the growth index of linear matter perturbations

We propose a parametrization for the growth index of the linear matter perturbations, $γ(z)=γ_0+\frac{z}{1+z}γ_1$. The growth factor of the perturbations parameterized as $Ω_m^γ$ is analyzed for both the $w$CDM model and the DGP model with our proposed form for $γ$. We find that $γ_1$ is negative for the $w$CDM model but is positive for the DGP model. Thus it provides another signature to discriminate them. We demonstrate that $Ω_m^γ$ with $γ$ taking our proposed form approximates the growth factor very well both at low and high redshfits for both kinds of models. In fact, the error is below 0.03% for the $Λ$CDM model and 0.18% for the DGP model for all redshifts when $Ω_{m0}=0.27$. Therefore, our parametrization may be robustly used to constrain the growth index of different models with the observational data which include points for redshifts ranging from 0.15 to 3.8, thus providing discriminative signatures for different models.

gr-qc↗

arXiv2009

Inverse volume corrections to emergent tachyonic inflation in loop quantum cosmology

The emergent model in the context of loop quantum cosmology with a tachyon scalar field is studied. We find that there is a center equilibrium point in the semiclassical region and a saddle point in the classical region. If the potential of the tachyon field satisfies some conditions, the universe can stay at the center equilibrium point past-eternally and then oscillate infinitely around this point with the tachyon climbing up its potential. Once the potential reaches a critical value, these two equilibrium points coincide with each other and the oscillation phase is broken by an emergent inflation. In order to obtain a successful emergent tachyon inflation, a constraint on $\dotϕ^2$ of tachyon is required.

astro-ph.CO↗

arXiv2009

The growth of linear perturbations in the DGP model

We study the linear growth of matter perturbations in the DGP model with the growth index $γ$ as a function of redshift. At the linear approximation: $γ(z)\approxγ_0+γ_0^\prime z $, we find that, for $0.2\leqΩ_{m,0}\leq0.35$, $γ_0$ takes the value from 0.658 to 0.671, and $γ_0^\prime$ ranges from 0.035 to 0.042. With three low redshift observational data of the growth factor, we obtain the observational constraints on $γ_0$ and $γ_0'$ for the $ΛCDM$ and DGP models and find that the observations favor the $ΛCDM$ model but at the $1σ$ confidence level both the $ΛCDM$ and DGP models are consistent with the observations.

gr-qc↗

arXiv2008

Dynamics of interacting phantom scalar field dark energy in Loop Quantum Cosmology

We study the dynamics of a phantom scalar field dark energy interacting with dark matter in loop quantum cosmology (LQC). Two kinds of coupling of the form $α{ρ_m}{\dotϕ}$ (case I) and $3βH (ρ_ϕ+ρ_m)$ (case II) between the phantom energy and dark matter are examined with the potential for the phantom field taken to be exponential. For both kinds of interactions, we find that the future singularity appearing in the standard FRW cosmology can be avoided by loop quantum gravity effects. In case II, if the phantom field is initially rolling down the potential, the loop quantum effect has no influence on the cosmic late time evolution and the universe will accelerate forever with a constant energy ratio between the dark energy and dark matter.

gr-qc↗

arXiv2008

Cosmological evolution of interacting phantom (quintessence) model in Loop Quantum Gravity

The dynamics of interacting dark energy model in loop quantum cosmology (LQC) is studied in this paper. The dark energy has a constant equation of state $w_x$ and interacts with dark matter through a form $3cH(ρ_x+ρ_m)$. We find for quintessence model ($w_x>-1$) the cosmological evolution in LQC is the same as that in classical Einstein cosmology; whereas for phantom dark energy ($w_x<-1$), although there are the same critical points in LQC and classical Einstein cosmology, loop quantum effect reduces significantly the parameter spacetime ($c, w_x$) required by stability. If parameters $c$ and $w_x$ satisfy the conditions that the critical points are existent and stable, the universe will enter an era dominated by dark energy and dark matter with a constant energy ratio between them, and accelerate forever; otherwise it will enter an oscillatory regime. Comparing our results with the observations we find at $1σ$ confidence level the universe will accelerate forever.

astro-ph↗

arXiv2008

Brownian motion of a charged test particle driven by vacuum fluctuations near a dielectric half-space

We study the Brownian motion of a charged test particle driven by quantum electromagnetic fluctuations in the vacuum region near a non-dispersive and non-absorbing dielectric half-space and calculate the mean squared fluctuations in the velocity of the test particle. Our results show that a nonzero susceptibility of the dielectrics has its imprints on the velocity dispersions of the test particles. The most noteworthy feature in sharp contrast to the case of an idealized perfectly conducting interface is that the velocity dispersions in the parallel directions are no longer negative and does not die off in time, suggesting that the potentially problematic negativeness of the dispersions in those directions in the case of perfect conductors is just a result of our idealization and does not occur for real material boundaries.

quant-ph↗

arXiv2008

Probing the cosmic acceleration history and the properties of dark energy from the ESSENCE supernova data with a model independent method

With a model independent method the expansion history $H(z)$, the deceleration parameter $q(z)$ of the universe and the equation of state $w(z)$ for the dark energy are reconstructed directly from the 192 Sne Ia data points, which contain the new ESSENCE Sne Ia data and the high redshift Sne Ia data. We find that the evolving properties of $q(z)$ and $w(z)$ reconstructed from the 192 Sne Ia data seem to be weaker than that obtained from the Gold set, but stronger than that from the SNLS set. With a combination of the 192 Sne Ia and BAO data, a tight constraint on $Ω_{m0}$ is obtained. At the $1σ$ confidence level $Ω_{m0}=0.278^{+0.024}_{-0.023}$, which is highly consistent with that from the Gold+BAO and SNLS+BAO.

astro-ph↗

arXiv2007

Reconstructing the properties of dark energy from recent observations

We explore the properties of dark energy from recent observational data, including the Gold Sne Ia, the baryonic acoustic oscillation peak from SDSS, the CMB shift parameter from WMAP3, the X-ray gas mass fraction in cluster and the Hubble parameter versus redshift. The $ΛCDM$ model with curvature and two parameterized dark energy models are studied. For the $ΛCDM$ model, we find that the flat universe is consistent with observations at the $1σ$ confidence level and a closed universe is slightly favored by these data. For two parameterized dark energy models, with the prior given on the present matter density, $Ω_{m0}$, with $Ω_{m0}=0.24$, $Ω_{m0}=0.28$ and $Ω_{m0}=0.32$, our result seems to suggest that the trend of $Ω_{m0}$ dependence for an evolving dark energy from a combination of the observational data sets is model-dependent.

astro-ph↗

arXiv2007

Constraints on the unified dark energy-dark matter model from latest observational data

The generalized Chaplygin gas (GCG), is studied in this paper by using the latest observational data including 182 gold sample type Ia supernovae (Sne Ia) data, the ESSENCE Sne Ia data, the distance ratio from $z=0.35$ to $z=1089$ (the redshift of decoupling), the CMB shift parameter and the Hubble parameter data. Our results rule out the standard Chaplygin gas model ($α=1$) at the 99.7% confidence level, but allow for the $λCDM$ model ($α=0$) at the 68.3% confidence level. At a 95.4% confidence level, we obtain $w=-0.74_{-0.09}^{+0.10}$ and $α=-0.14_{-0.19}^{+0.30}$. In addition, we find that the phase transition from deceleration to acceleration occurs at redshift $z_{q=0}\sim 0.78-0.89$ at a $1σ$ confidence level for the GCG model.

astro-ph↗