Can we remove the systematic error due to isotropic inhomogeneities?
  Usually, we assume that there is no inhomogeneity isotropic in terms of our
location in our uni- verse. This assumption has not been observationally
confirmed yet in sufficient accuracy, and we need to consider the possibility
that there are non-negligible large-scale isotropic inhomogeneities in our
universe. The existence of large-scale isotropic inhomogeneities affects the
determination of the cosmological parameters. In particular, from only the
distance-redshift relation, we can not dis- tinguish the inhomogeneous
isotropic universe model from the homogeneous isotropic one, because of the
ambiguity in the cosmological parameters. In this paper, in order to avoid such
ambiguity, we consider three observables, the distance-redshift relation, the
fluctuation spectrum of the cosmic microwave background radiation(CMBR) and the
scale of the baryon acoustic oscillation(BAO), and compare these observables in
two universe models; One is the inhomogeneous isotropic uni- verse model with
the cosmological constant and the other is the homogeneous isotropic universe
model with the dark energy other than the cosmological constant. We show that
these two universe models can not predict the same observational data of all
three observables but the same ones of only two of three, as long as the
perturbations are adiabatic. In principle, we can distinguish the inhomogeneous
isotropic universe from the homogeneous isotropic one through appropriate three
observables, if the perturbations are adiabatic.
