Yuanxing Gui

Letter: The Real Scalar Field in Schwarzschild-de Sitter Spacetime

In this paper, the real scalar field equation in Schwarzschild-de Sitter spacetime is solved numerically with high precision. A method called ‘polynomial’ approximation is introduced to derive the relation between the tortoise coordinate x and the radius r. This method is different from the ‘tangent’ approximation [1] and leads to more accurate results. The Nariai black hole is then discussed in details. We find that the wave function is harmonic only near the horizons as I. Brevik and B. Simonsen [1] found. However the wave function is not harmonic in the region of the potential peak, with amplitude increasing instead. Furthermore, we also find that, when the cosmological constant decreases, the potential peak increases, and the maximum wave amplitude increases.

PARAMETRIZATION OF TACHYON FIELD

We assume that universe is dominated by non-relativistic matter and tachyon field and reconstruct the potential of tachyon field directly from the effective equation of state (EOS) of dark energy. We apply the method to four known parametrization of equation of state and discuss the general features of the resulting potentials.We investigate matter collineations of plane symmetric spacetimes when the energy-momentum tensor is degenerate. There exists three interesting cases where the group of matter collineations is finite-dimensional. The matter collineations in these cases are either four, six or ten in which four are isometries and the rest are proper.

A more general interacting model of holographic dark energy

Abstract 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.

THE UNIFIED EQUATION OF STATE FOR DARK MATTER AND DARK ENERGY

We assume that dark matter and dark energy satisfy the unified equation of state: p = B(z)ρ, with p = pdE, ρ = ρdm+ρdE, where the pressure of dark matter pdm = 0 has been taken into account. A special function

Double Structures and Multiple Symmetry Groups for the Reduced 4-Dimensional String Background Equations

B=-\frac{A}{(1+z)^{\alpha}}

PARTITION FUNCTION OF THE GAS-LIQUID COEXISTENT SYSTEM

is presented, which can well describe the evolution of the universe. In this model, the universe will end up with a Big Rip. By further simple analysis, we know other choices of the function B can also describe the universe but lead to a different doomsday.

REVISED EQUATION OF STATE FOR A SIMPLE FLUID BASED ON VAN DE WAALS EQUATION

By using the extended double complex method proposed previously, the 1-loop string background equations with axion and dilaton fields in 4 dimensions with two commuting Killing symmetries and δc = 0 are reduced essentially to two double Ernst σ-models. Then the string Geroch group acting on the solution space is extended to a multi-fold version of a semidirect product of the string Geroch group and the Virasoro group. The usual string Geroch group is just one component of a subgroup in the multi-fold semidirect product group. It is also found that a dobule Z2 symmetry exists for every case of the 4-dimensional reduced string equations and for most of the cases here, this Z2 symmetry is new and cannot be obtained in the usual (non-double) scheme. These results show that the reduced string background equations considered possess more and richer symmetry structures than previously expected. Moreover, a double form of string soliton method is briefly described and, as an application, a multiple family of soliton solutions of the considered reduced string equations is given, which shows that the double method is more effective.

Quasinormal modes of a Schwarzschild black hole surrounded by free static spherically symmetric quintessence: electromagnetic perturbations

In this article the equilibrious gas-liquid coexistent system is studied, and a new expression of partition function (PF) corresponding to the two-phase region is derived. Based on this expression, the horizontal line in the isotherm of pressure versus volume is obtained naturally for a finite particle system (i.e., without the necessity of taking the thermodynamic limit). Extending this PF, we can gain a unitive form of the one-component fluid in any system (i.e., one-phase or multi-phase). Then the whole isotherm will have reasonable statistical foundation. The VDW fluid system is discussed as a concrete example.

THE SCALAR FIELD IN EXTREME REISSNER–NORDSTRÖM–DE SITTER SPACE

In this article, the equation of state for a simple fluid is studied. A new universal equation of state is presented from statistical physics. It gives better properties for a liquid-gas coexisting system. Also, a reduced equation of state correlated with the reduced form of this universal one is obtained. It results in a phase diagram which fits the Guggenheim expressions perfectly well, and further the correct critical exponent β.