Second-order perturbations and Cardassian cosmology

초록

Since the universe is endowed with small irregularities at all kinds of different length scales, they constitute a portion, though expected to be small, of energy density and pressure of the universe, and thereby can affect the overall expansion rate of the universe. In the companion work to be presented in the present KPS meeting we are to show how to calculate the averaged irregularities in quantities like energy density and pressure up to second-order of general-relativistic perturbation theory. We apply the results to consider the effects of irregularities on the expansion rate of the universe in some recent cosmological models like Cardassian model and Chaplygin model with unusual euqation of state. We discuss the constraints on the parameters of these models in regard to the growth of irregularities as the universe expands.