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 α which implements the anisotropy between the four dimensional spacetime and the extra dimension. We find that a range of value of the parameter α can address the current dark energy density compared to the Planck energy density. Constraining the parameter α 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 α>−2.05 for Planck data and α>−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_eff) at present and the variation of G_eff since the epoch of recombination to be consistent with observation.