  First the fluctuation energy is derived from the adiabatic random
fluctuations due to the second-order perturbation theory, and the evolutionary
relation for it is expressed in the form of rho_f = rho_f (rho), where rho and
rho_f are the densities of ordinary dust and the fluctuation energy,
respectively. The pressureless matter as a constituent of the universe at the
later stage is assumed to consist of ordinary dust and the fluctuation energy.
Next, cosmological models including the fluctuation energy as a kind of dark
matter are derived using the above relation, and it is found that the Hubble
parameter and the other model parameters in the derived models can be
consistent with the recent observational values. Moreover, the perturbations of
rho and rho_f are studied.
