arXiv subjects

Hao Wei

Publications and source records attributed to Hao Wei.

At least 127 records · Page 7Linked to original sources

arXiv2009

Entropy-Corrected Holographic Dark Energy

The holographic dark energy (HDE) is now an interesting candidate of dark energy, which has been studied extensively in the literature. In the derivation of HDE, the black hole entropy plays an important role. In fact, the entropy-area relation can be modified due to loop quantum gravity or other reasons. With the modified entropy-area relation, we propose the so-called ``entropy-corrected holographic dark energy'' (ECHDE) in the present work. We consider many aspects of ECHDE and find some interesting results. In addition, we briefly consider the so-called ``entropy-corrected agegraphic dark energy'' (ECADE).

gr-qc↗

arXiv2009

Reconstructing the Cosmic Expansion History up to Redshift z=6.29 with the Calibrated Gamma-Ray Bursts

Recently, Gamma-Ray Bursts (GRBs) were proposed to be a complementary cosmological probe to type Ia supernovae (SNIa). GRBs have been advocated to be standard candles since several empirical GRB luminosity relations were proposed as distance indicators. However, there is a so-called circularity problem in the direct use of GRBs. Recently, a new idea to calibrate GRBs in a completely cosmology independent manner has been proposed, and the circularity problem can be solved. In the present work, following the method proposed by Liang {\it et al.}, we calibrate 70 GRBs with the Amati relation using 307 SNIa. Then, following the method proposed by Shafieloo {\it et al.}, we smoothly reconstruct the cosmic expansion history up to redshift $z=6.29$ with the calibrated GRBs. We find some new features in the reconstructed results.

astro-ph↗

arXiv2009

Relaxing the Cosmological Constraints on Unparticle Dark Component

Unparticle physics has been an active field since the seminal work of Georgi. Recently, many constraints on unparticles from various observations have been considered in the literature. In particular, the cosmological constraints on the unparticle dark component put it in a serious situation. In this work, we try to find a way out of this serious situation, by including the possible interaction between dark energy and the unparticle dark component.

gr-qc↗

arXiv2009

Modified Holographic Dark Energy

In this work, motivated by the energy bound suggested by Cohen {\it et al.}, we propose the modified holographic dark energy (MHDE) model. Choosing the IR cut-off $L=R_{\rm CC}$ and considering the parameterizations $n^2=2-λa$, $n^2=2-3λa^2/(1+3a^2)$ and $n^2=2-λa^2/(β+a^2)$, we derive all the physical quantities of the non-saturated MHDE model analytically. We find that the non-saturated MHDE models with the parameterizations $n^2=2-λa$ and $n^2=2-3λa^2/(1+3a^2)$ are single-parameter models in practice. Also, we consider the cosmological constraints on the non-saturated MHDE, and find that it is well consistent with the observational data.

gr-qc↗

arXiv2009

Cosmological Models and Latest Observational Data

In this note, we consider the observational constraints on some cosmological models by using the 307 Union type Ia supernovae (SNIa), the 32 calibrated Gamma-Ray Bursts (GRBs) at $z>1.4$, the updated shift parameter $R$ from WMAP 5-year data (WMAP5), and the distance parameter $A$ of the measurement of the baryon acoustic oscillation (BAO) peak in the distribution of SDSS luminous red galaxies with the updated scalar spectral index $n_s$ from WMAP5. The tighter constraints obtained here update the ones obtained previously in the literature.

astro-ph↗

arXiv2009

Interacting Agegraphic Dark Energy

A new dark energy model, named "agegraphic dark energy", has been proposed recently, based on the so-called Károlyházy uncertainty relation, which arises from quantum mechanics together with general relativity. In this note, we extend the original agegraphic dark energy model by including the interaction between agegraphic dark energy and pressureless (dark) matter. In the interacting agegraphic dark energy model, there are many interesting features different from the original agegraphic dark energy model and holographic dark energy model. The similarity and difference between agegraphic dark energy and holographic dark energy are also discussed.

hep-th↗

arXiv2008

How to Distinguish Dark Energy and Modified Gravity?

The current accelerated expansion of our universe could be due to an unknown energy component (dark energy) or a modification to general relativity (modified gravity). In the literature, it has been proposed that combining the probes of the cosmic expansion history and growth history can distinguish between dark energy and modified gravity. In this work, without invoking non-trivial dark energy clustering, we show that the possible interaction between dark energy and dark matter could make the interacting dark energy model and the modified gravity model indistinguishable. An explicit example is also given. Therefore, it is required to seek some complementary probes beyond the ones of cosmic expansion history and growth history.

astro-ph↗

arXiv2008

Growth Index of DGP Model and Current Growth Rate Data

Recently, some efforts focus on differentiating dark energy and modified gravity with the growth function $δ(z)$. In the literature, it is useful to parameterize the growth rate $f\equiv d\lnδ/d\ln a=Ω_m^γ$ with the growth index $γ$. In this note, we consider the general DGP model with any $Ω_k$. We confront the growth index of DGP model with currently available growth rate data and find that the DGP model is still consistent with it. This implies that more and better growth rate data are required to distinguish between dark energy and modified gravity.

astro-ph↗

arXiv2008

Cosmological Constraints on New Agegraphic Dark Energy

In this work, we consider the cosmological constraints on the new agegraphic dark energy (NADE) proposed in arXiv:0708.0884, by using the observational data of type Ia supernovae (SNIa), the shift parameter from cosmic microwave background (CMB) and the baryon acoustic oscillation (BAO) peak from large scale structures (LSS). Thanks to its special analytic features in the radiation-dominated and matter-dominated epochs, NADE is a single-parameter model in practice because once the single model parameter $n$ is given, all other physical quantities of NADE can be determined correspondingly. The joint analysis gives the best-fit value (with $1σ$ uncertainty) $n=2.716^{+0.111}_{-0.109}$, and the derived $Ω_{m0}$, $Ω_{q0}$ and $w_{q0}$ (with $1σ$ uncertainties) are $0.295^{+0.020}_{-0.020}$, $0.705^{+0.020}_{-0.020}$ and $-0.794^{+0.006}_{-0.005}$, respectively. In addition, we find that the coincidence problem could be solved naturally in the NADE model provided that $n$ is of order unity.

astro-ph↗

arXiv2008

A New Model of Agegraphic Dark Energy

In this note, we propose a new model of agegraphic dark energy based on the Károlyházy relation, where the time scale is chosen to be the conformal time $η$ of the Friedmann-Robertson-Walker (FRW) universe. We find that in the radiation-dominated epoch, the equation-of-state parameter of the new agegraphic dark energy $w_q=-1/3$ whereas $Ω_q=n^2a^2$; in the matter-dominated epoch, $w_q=-2/3$ whereas $Ω_q=n^2a^2/4$; eventually, the new agegraphic dark energy dominates; in the late time $w_q\to -1$ when $a\to\infty$, and the new agegraphic dark energy mimics a cosmological constant. In every stage, all things are consistent. The confusion in the original agegraphic dark energy model proposed in arXiv:0707.4049 disappears in this new model. Furthermore, $Ω_q\ll 1$ is naturally satisfied in both radiation-dominated and matter-dominated epochs where $a\ll 1$. In addition, we further extend the new agegraphic dark energy model by including the interaction between the new agegraphic dark energy and background matter. In this case, we find that $w_q$ can cross the phantom divide.

astro-ph↗

arXiv2007

Statefinder Diagnostic and w-w' Analysis for the Agegraphic Dark Energy Models without and with Interaction

A new dark energy model, named as ``agegraphic dark energy'', has been proposed by one of us (R. G. Cai) in arXiv:0707.4049, based on the Károlyházy uncertainty relation, which arises from the quantum mechanics together with general relativity. Then, in arXiv:0707.4052, it has been extended by including the interaction between the agegraphic dark energy and the pressureless (dark) matter. In this note, we investigate the agegraphic dark energy models without and with interaction by means of statefinder diagnostic and w-w' analysis.

gr-qc↗

arXiv2007

Interacting Energy Components and Observational $H(z)$ Data

In this note, we extend our previous work [Phys. Lett. B 644, 7 (2007), astro-ph/0609597], and compare eleven interacting dark energy models with different couplings to the observational $H(z)$ data. However, none of these models is better than the simplest $Λ$CDM model. This implies that either more exotic couplings are needed in the cosmological models with interaction between dark energy and dust matter, or {\em there is no interaction at all}. We consider that this result is disadvantageous to the interacting dark energy models studied extensively in the literature.

astro-ph↗

arXiv2007

Cheng-Weyl Vector Field and its Cosmological Application

Weyl's idea on scale invariance was resurrected by Cheng in 1988. The requirement of local scale invariance leads to a completely new vector field, which we call the ``Cheng-Weyl vector field''. The Cheng-Weyl vector field couples only to a scalar field and the gravitational field naturally. It does not interact with other known matters in the standard model of particle physics. In the present work, the (generalized) Cheng-Weyl vector field coupled with the scalar field and its cosmological application are investigated. A mixture of the scalar field and a so-called ``cosmic triad'' of three mutually orthogonal Cheng-Weyl vector fields is regarded as the dark energy in the universe. The cosmological evolution of this ``mixed'' dark energy model is studied. We find that the effective equation-of-state parameter of the dark energy can cross the phantom divide $w_{de}=-1$ in some cases; the first and second cosmological coincidence problems can be alleviated at the same time in this model.

astro-ph↗

arXiv2007

Age Problem in the Holographic Dark Energy Model

In this note, we test the original holographic dark energy model with some old high redshift objects. The main idea is very simple: the universe cannot be younger than its constituents. We find that the original holographic dark energy model can be ruled out, unless a lower Hubble constant is taken.

astro-ph↗

arXiv2007

Dynamics of Quintom and Hessence Energies in Loop Quantum Cosmology

In the present work, we investigate the universe dominated by quintom or hessence energies in Loop Quantum Cosmology (LQC). Interestingly enough, we find that there are some stable attractors in these two cases. In the case of quintom, all stable attractors have the feature of decelerated expansion. In the case of hessence, most of stable attractors have the feature of decelerated expansion while one stable attractor can have decelerated or accelerated expansion depend on the model parameter. In all cases, the equation-of-state parameter (EoS) of all stable attractors are larger than -1 and there is no singularity in the finite future. These results are different from the dynamics of phantom in LQC, or the ones of phantom, quintom and hessence in classical Einstein gravity.

gr-qc↗

arXiv2007

Age constraints on the Agegraphic Dark Energy Model

We investigate the age constraint on the agegraphic dark energy model by using two old galaxies (LBDS 53W091 and LBDS 53W069) and the old high redshift quasar APM 08279+5255. We find that the agegraphic dark energy model can easily accommodate LBDS 53W091 and LBDS 53W069. To accommodate APM 08279+5255, one can take the reduced Hubble parameter as large as h=0.64, when the fraction matter energy density $Ω_{m0}\approx 0.22$.

astro-ph↗

arXiv2007

Reconstruction of Hessence Dark Energy and the Latest Type Ia Supernovae Gold Dataset

Recently, many efforts have been made to build dark energy models whose equation-of-state parameter can cross the so-called phantom divide $w_{de}=-1$. One of them is the so-called hessence dark energy model in which the role of dark energy is played by a non-canonical complex scalar field. In this work, we develop a simple method based on Hubble parameter $H(z)$ to reconstruct the hessence dark energy. As examples, we use two familiar parameterizations for $H(z)$ and fit them to the latest 182 type Ia supernovae Gold dataset. In the reconstruction, measurement errors are fully considered.

astro-ph↗

arXiv2006

Observational $H(z)$ Data and Cosmological Models

In this work, we confront ten cosmological models with observational $H(z)$ data. The possible interaction between dark energy and dust matter is allowed in some of these models. Also, we consider the possibility of (effective) equation-of-state parameter (EoS) crossing -1. We find that the best models have an oscillating feature for both $H(z)$ and EoS, with the EoS crossing -1 around redshift $z\sim 1.5$.

astro-ph↗