Observational Constraints On Cosmology

During the last ten to twenty years, cosmology has grown into a data-driven from a data-starved science. Several key pa-rameters of the universe(such as matter density parameter Ωm,0and decelerate parameter q0), have now been measured more ac-curately than10%. Amazingly, the observations of Type la su-pernovae (SNe Ia) revealed that, instead of slowing down, the ex-pansion of the universe goes on at an ever increasing rate. On the basis of observations, people infer that there is an exotic matter-energy component with negative pressure, named dark energy, which makes up more than two thirds of the total matter-energy content of our universe. It is generally agreed that comprehend-ing the nature of the dark energy is one of the biggest challenges for the modern theoretical physics. In order to avoid this exotic component, the idea that the existing laws of gravity do not hold any more in large scale has been proposed. The theories which modify the Einstein gravity law can also explain the accelerating expansion of universe without dark energy.So far, large numbers of cosmological models have been proposed. Meanwhile, more and more datasets with high qual-itv have been obtained from astronomical observations. These datasets hold the promise for unveiling many properties of the mysterious dark energy component, or understanding the gravity laws in large scale. Therefore, it is necessary to connect the mod- els with observations. In this paper, we first study the constraints on several popular models with latest observations. We find that the ACDM is preferred by most observations (SNe Ia, the data derived from the combination of cosmic microwave background and baryon acoustic oscillation, and the Hubble parameters ver-sus redshift data). Howeve the DGP model is most favored when only the latest SNe la are considered.Secondly, with the help of parameterizations of equation of state (EoS), we probe the cosmic acceleration using observations. We find that the cosmic acceleration may be slowing down, or even our universe may have already entered a decelerating ex-panding stage. However, these are somewhat dependent on the parametric forms and the observations.Finally, we test the cosmic distance-duality (DD) relation with data from SNe la and galaxy clusters in a cosmological-model-independent way. We find that the DD relation is gener-ally consistent with observations, and both the sample of galaxy cluster and the Chandra calibration exert influences on the DD relation test. Besides, we study the cosmic opacity with the help of the DD relation and find that the observations favor a trans-parent universe with cosmological constant Λ﹥0.