Abstract
We constrain a unified dark matter (UDM) model from the latest observational data. This model assumes that the dark sector is degenerate. Dark energy and dark matter are the same component. It can be described by an affine equation of state PX=p0+αρX. Our data set contains the newly revised H(z) data, type Ia supernovae (SNe Ia) from Union2 set, baryonic acoustic oscillation (BAO) observation from the spectroscopic Sloan Digital Sky Survey (SDSS) data release 7 (DR7) galaxy sample, as well as the cosmic microwave background (CMB) observation from the 7-year Wilkinson Microwave Anisotropy Probe (WMAP7) results. By using the Markov Chain Monte Carlo (MCMC) method, we obtain the results in a flat universe: ΩΛ=0.719−0.0305+0.0264(1σ)−0.0458+0.0380(2σ), α=1.72−4.79+3.92(1σ)−7.30+5.47(2σ)(×10−3), Ωbh2=0.0226−0.0011+0.0011(1σ)−0.0015+0.0016(2σ). Moreover, when considering a non-flat universe, ΩΛ=0.722−0.0447+0.0362(1σ)−0.0634+0.0479(2σ), α=0.242−0.775+0.787(1σ)−1.03+1.10(2σ)(×10−2), Ωbh2=0.0227−0.0014+0.0015(1σ)−0.0018+0.0021(2σ), Ωk=−0.194−1.85+2.02(1σ)−2.57+2.75(2σ)(×10−2). These give a more stringent results than before. We also give the results from other combinations of these data for comparison. The observational Hubble parameter data can give a more stringent constraint than SNe Ia. From the constraint results, we can see the parameters α and Ωk are very close to zero, which means a flat universe is strongly supported and the speed of sound of the dark sector seems to be zero.
Highlights
Cosmic acceleration is one of the most striking discoveries in modern cosmology [1]
A unified dark matter model was proposed which assumes that dark matter and dark energy are from a same dark component [13]
We combine H(z), SNe Ia, cosmic microwave background (CMB) and baryonic acoustic oscillation (BAO) data to give a global fitting on determining the parameters of UDM model
Summary
Cosmic acceleration is one of the most striking discoveries in modern cosmology [1]. Many works have been done to explain this unexpected phenomenon. The ”coincidence” problem and the ”fine-tuning” problem [10] From this standard model, the flat universe consists of ∼ 4% baryons, ∼ 23% dark matter, ∼ 73% dark energy [11]. A unified dark matter model was proposed which assumes that dark matter and dark energy are from a same dark component [13]. Stern et al [25] revised these data at 11 redshifts from the differential ages of red-envelope galaxies. We use the Markov chain Monte Carlo (MCMC) method to give constraints on the unified dark matter model from the latest data including the observational Hubble parameter data.
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