Constraints on smoothness parameter and dark energy using observational H(z) data

With large-scale homogeneity, the universe is locally inhomogeneous, clustering into stars, galaxies and larger structures. Such property is described by the smoothness parameter alpha which is defined as the proportion of matter in the form of intergalactic medium. If we consider the inhomogeneities over a small scale, there should be modifications of the cosmological distances compared to a homogenous model. Dyer and Roeder developed a second-order ordinary differential equation (D-R equation) that describes the angular diameter distance-redshift relation for inhomogeneous cosmological models. Furthermore, we may obtain the D-R equation for observational H(z) data (OHD). The density-parameter Omega(M), the state of dark energy omega, and the smoothness-parameter alpha are constrained by a set of OHD in a spatially flat ACDM universe as well as a spatially flat XCDM universe. By using a chi(2) minimization method, we get alpha = 0.81(-0.20)(+0.19) and Omega(M) = 0.32(-0.06)(+0.12) at the 1 sigma confidence level. If we assume a Gaussian prior of Omega(M) = 0.26 +/- 0.1, we get alpha = 0.93(-0.19)(+0.07) and Omega M = 0.31(-0.05)(+0.06). For the XCDM model, a is constrained to alpha >= 0.80 but omega is weakly constrained around 1, where w describes the equation of state of the dark energy (p(X) = omega rho(X)). We conclude that OHD constrains the smoothness parameter more effectively than the data of SNe Ia and compact radio sources.http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcApp=PARTNER_APP&SrcAuth=LinksAMR&KeyUT=WOS:000287644700001&DestLinkType=FullRecord&DestApp=ALL_WOS&UsrCustomerID=8e1609b174ce4e31116a60747a720701Astronomy & AstrophysicsSCI(E)中国科技核心期刊(ISTIC)4ARTICLE2125-1361