arXiv subjects
Publications and source records attributed to Xin-Zhou Li.
The Ricci dark energy (RDE) proposed to explain the accelerating expansion of the universe requires its parameter $α< 1$, whose value will determine the behavior of RDE. In this Letter, we study the scalar perturbation of RDE with and without matter in the universe, and we find that in both cases, the perturbation is stable if $α> 1/3$, which gives a lower bound for $α$ theoretically.
The viscous Cardassian cosmology is discussed, assuming that there is a bulk viscosity in the cosmic fluid. The dynamical analysis indicates that there exists a singular curve in the phase diagram of viscous Cardassian model. In the viscous PL model, the equation-of-state parameter $w_{k}$ is no longer a constant and it can cross the cosmological constant divide $w_Λ=-1$, in contrast with same problem of the ordinary PL model. Other models possess with similar characteristics. For MP and exp models, $w_{k}$ evolves more near -1 than the case without viscosity. The bulk viscosity also effect the virialization process of a collapse system in the universe: $\frac{R_{vir}}{R_{ta}}$ is increasingly large when the bulk viscosity is increasing. In other words, the bulk viscosity retards the progress of collapse system. In addition, we fit the viscous Cardassian models to current type Ia supernovae data and give the best fit value of the model parameters including the bulk viscosity coefficient $τ$.
We generalize the field theory of global monopole to Dirac-Born-Infeld(DBI) field and investigate the gravitational property of a DBI global monopole in four-dimensional spherically symmetric spacetime. The coupled equations for the metric and the DBI scalar field are solved asymptotically and numerically. It is found that, just as a canonical global monopole, the gravitational effect of DBI global monopole is equivalent to that of a deficit solid angle in the metric plus a negative mass at the origin. However, compared with a canonical global monopole, for the same false vacuum and symmetry breaking scale, a DBI global monopole has a relatively smaller core and a larger absolute value of effective mass. Thus, it can give out a larger deflect angle when the light passing by. Especially, when the scale of warp factor is small enough, the effective mass of a DBI global monopole does not depend apparently on the value of the false vacuum, which is qualitatively different from that of a canonical global monopole.
In this paper, we revisit the parameterizations of the equation of state of dark energy and point out that comparing merely the $χ^2$ of different fittings may not be optimal for choosing the "best" parametrization. Another figure of merit for evaluating different parametrizations based on the area of the $w(z) - z$ band is proposed. In light of the analysis of some two-parameter parameterizations and models based on available SNIa data, the area of $w(z)-z$ band seems to be a good figure of merit, especially in the situation that the value of $χ^2_{\rm min}$ for different parametrizations are very close. Therefore, we argue that both the area of the $w(z)-z$ band and $χ^2_{\rm min}$ should be synthetically considered for choosing a better parametrization of dark energy in the future experiments.
In this paper, we investigate the evolution of classical wave propagation in the canonical acoustic black hole by numerical method and discuss the details of tail phenomenon. The oscillating frequency and damping time scale both increase with the angular momentum $l$. For the lower $l$, numerical results show the lowest WKB approximation gives the most reliable result. We also find that time scale of the interim region from ringing to tail is not affected obviously by changing $l$.