Lixin Xu, Yuting Wang, Hyerim Noh
As known above 90% of the energy content in our universe is made of unknown
dark component. Usually this dark fluid is separated into two energy
components: dark matter and dark energy. However, maybe it is a mixture of dark
matter and dark energy components, or just one exotic unknown fluid. This
property is dubbed as dark degeneracy. With this motivation, in this paper, a
unified dark fluid with constant adiabatic sound speed $c_s^2=\alpha$ in the
range $[0,1]$ is studied. At first, via the energy conservation equation, its
energy density, $\rho_d/\rho_{d0}=(1-B_s)+B_s a^{-3(1+\alpha)}$ where $B_s$ is
related to integration constant from energy conservation equation as another
model parameter, is presented. Then by using Markov Chain Monte Carlo method
with current available cosmic observational data sets which include type Ia
supernova Union 2, baryon acoustic oscillation and WMAP 7-year data of cosmic
background radiation, we show that small values of $\alpha$ are favored in this
unified dark fluid model.
View original:
http://arxiv.org/abs/1112.3701
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