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1. chinaXiv:201709.00130 [pdf]

Constraints on the DGP Model from Recent Supernova Observations and Baryon Acoustic Oscillations

Zong-Kuan Guo , Zong-Hong Zhu , J.S. Alcaniz , Yuan-Zhong Zhang; Zong-Hong Zhu; J.S. Alcaniz; Yuan-Zhong Zhang
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

Although there is mounting observational evidence that the expansion of our universe is undergoing a late-time acceleration, the mechanism for this acceleration is yet unknown. In the so-called Dvali-Gabadadze-Porrati (DGP) model this phenomena is attributed to gravitational leakage into extra dimensions. In this work, we mainly focus our attention to the constraints on the model from the gold sample of type Ia supernovae (SNeIa), the first year data from the Supernova Legacy Survey (SNLS) and the baryon acoustic oscillation (BAO) peak found in the Sloan Digital Sky Survey (SDSS). At 99.73% confidence level, the combination of the three databases provides m = 0.270+0.018?0.017 and rc = 0.216+0.012?0.013 (hence a spatially closed universe with k = ?0.350+0.080?0.083), which seems to be in contradiction with the most recent WMAP results indicating a flat universe. Based on this result, we also estimated the transition redshift (at which the universe switches from deceleration to acceleration) to be 0.70 < zq=0 < 1.01, at 2#27;confidence level.

submitted time 2017-09-27 Hits1867Downloads963 Comment 0

2. chinaXiv:201709.00131 [pdf]

A Tracker Solution for a Holographic Dark Energy Model

Hui Li,b; Zong-Kuan Guo; Yuan-Zhong Zhang
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We investigate a kind of holographic dark energy model with the future event horizon the IR cutoff and the equation of state ?1. In this model, the constraint on the equation of state automatically specifies an interaction between matter and dark energy. With this interaction included, an accelerating expansion is obtained as well as the transition from deceleration to acceleration. It is found that there exists a stable tracker solution for the numerical parameter d > 1, and d smaller than one will not lead to a physical solution. This model provides another possible phenomenological framework to alleviate the cosmological coincidence problem in the context of holographic dark energy. Some properties of the evolution which are relevant to cosmological parameters are also discussed.

submitted time 2017-09-27 Hits2315Downloads1096 Comment 0

3. chinaXiv:201709.00132 [pdf]

Parametrization of K-essence and Its Kinetic Term

Hui Li; Zong-Kuan Guo; Yuan-Zhong Zhang
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We construct the non-canonical kinetic term of a k-essence field directly from the effective equation of state function wk(z), which describes the properties of the dark energy.Adopting the usual parametrizations of equation of state we numerically reproduce the shape of the non-canonical kinetic term and discuss some features of the constructed form of k-essence.

submitted time 2017-09-27 Hits1772Downloads991 Comment 0

4. chinaXiv:201709.00134 [pdf]

Observational Constraints on Variable Chaplygin Gas

Zong-Kuan Guo; Yuan-Zhong Zhang
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We investigate observational constraints on the variable Chaplygin gas model from the gold sample of type Ia supernova data and the recent measurements of the X-ray gas mass fractions in galaxy clusters. Combining these databases, we obtain a tight constraint on the two model parameters. Our results indicate that the original Chaplygin gas model is ruled out by the data at 99.7% confidence level.

submitted time 2017-09-27 Hits1595Downloads883 Comment 0

5. chinaXiv:201709.00135 [pdf]

Cosmology with a Variable Chaplygin Gas

Zong-Kuan Guo; Yuan-Zhong Zhang
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We consider a new generalized Chaplygin gas model that includes the original Chaplygin gas model as a special case. In such a model the generalized Chaplygin gas evolves as from dust to quiessence or phantom. We show that the background evolution for the model is equivalent to that for a coupled dark energy model with dark matter. The constraints from the current type Ia supernova data favour a phantom-like Chaplygin gas model.

submitted time 2017-09-27 Hits1685Downloads919 Comment 0

6. chinaXiv:201709.00136 [pdf]

Parametrization of Quintessence and Its Potential

Zong-Kuan Guo; Nobuyoshi Ohta; Yuan-Zhong Zhang
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

We develop a theoretical method of constructing the quintessence potential directly from the effective equation of state function w(z), which describes the properties of the dark energy. We apply our method to four parametrizations of equation of state parameter and discuss the general features of the resulting potentials. In particular, it is shown that the constructed quintessence potentials are all in the form of a runaway type.

submitted time 2017-09-27 Hits1716Downloads999 Comment 0

7. chinaXiv:201709.00044 [pdf]

QCD Sum Rule Analysis for the #3;b → #3;c Semileptonic Decay

Yuan-ben Dai; Chao-shang Huang; Ming-qiu Huang; Chun Liu
Subjects: Physics >> General Physics: Statistical and Quantum Mechanics, Quantum Information, etc.

The 1/mc and 1/mb corrections to the #3;b → #3;c semileptonic decay are analyzed by QCD sum rules. Within the framework of heavy quark effective theory, the subleading baryonic Isgur-Wise function of #3;b → #3;c has been calculated. It is shown that the corrections due to the 1/m Lagrangian insertion are negligibly small. The sizable 1/mQ effect to the decay lies only in the weak current. The decay spectrum and the branching ratio are given.

submitted time 2017-09-17 Hits946Downloads547 Comment 0

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