The Effect of Anisotropic Extra Dimension in Cosmology
  We consider five dimensional conformal gravity theory which describes an
anisotropic extra dimension. Reducing the theory to four dimensions yields
Brans-Dicke theory with a potential and a hidden parameter $z$ which implements
the anisotropy between the four dimensional spacetime and the extra dimension.
We find that a range of value of the parameter $z$ can address the current dark
energy density compared to the Planck energy density. Constraining the
parameter $z$ and the other cosmological model parameters using the recent
observational data consisting of the Hubble parameters, type Ia supernovae, and
baryon acoustic oscillations, together with the Planck or WMAP 9-year data of
the cosmic microwave background radiation, we find $z>-2.05$ for Planck data
and $z>-2.09$ for WMAP 9-year data at 95\% confidence level. We also obtained
constraints on the rate of change of the effective Newtonian constant~($G_{\rm
eff}$) at present and the variation of $G_{\rm eff}$ since the epoch of
recombination to be consistent with observation.
