Anzhong Wang

Cosmology with interaction between phantom dark energy and dark matter and the coincidence problem

We study a cosmological model in which phantom dark energy is coupled to dark matter by phenomenologically introducing a coupled term to the equations of motion of dark energy and dark matter. This term is parameterized by a dimensionless coupling function δ, the Hubble parameter and the energy density of dark matter, and it describes an energy flow between the dark energy and dark matter. We discuss two cases: one is the case where the equation of state ωe of the dark energy is a constant; the other is that where the dimensionless coupling function δ is a constant. We investigate the effect of the interaction on the evolution of the universe, the total lifetime of the universe and the ratio of the period when the universe is in the coincidence state to its total lifetime. It turns out that the interaction will produce significant deviation from the case without the interaction.

Cosmological perturbations in Horava-Lifshitz theory without detailed balance

In the Horava-Lifshitz theory of quantum gravity, two conditions - detailed balance and projectability - are usually assumed. The breaking of projectability simplifies the theory, but it leads to serious problems with the theory. The breaking of detailed balance leads to a more complicated form of the theory, but it appears to resolve some of the problems. Sotiriou, Visser and Weinfurtner formulated the most general theory of Horava-Lifshitz type without detailed balance. We compute the linear scalar perturbations of the FRW model in this form of HL theory. We show that the higher-order curvature terms in the action lead to a gravitational effective anisotropic stress on small scales. Specializing to a Minkowski background, we study the spin-0 scalar mode of the graviton, using a gauge-invariant analysis, and find that it is stable in both the infrared and ultraviolet regimes for 0{<=}{xi}{<=}2/3. However, in this parameter range the scalar mode is a ghost.

Reconstruction of the deceleration parameter and the equation of state of dark energy

The new 182 gold supernova Ia data, the baryon acoustic oscillation measurement and the shift parameter determined from the Sloan Digital Sky Survey, and the three-year Wilkinson Microwave Anisotropy Probe data are combined to reconstruct the dark energy equation of state parameter

Generalized Vaidya Solutions

w(z)

Scalar field perturbations in Horava-Lifshitz cosmology

and the deceleration parameter

Thick de Sitter 3 branes, dynamic black holes and localization of gravity

q(z)

Black holes and stars in Horava-Lifshitz theory with projectability condition

. We find that the strongest evidence of acceleration happens around the redshift

Exact scaling solutions and fixed points for general scalar field

z\ensuremath{\sim}0.2

Collapse of a scalar field in 2 + 1 gravity

and the stringent constraints on

Singularities in Horava-Lifshitz theory

w(z)