Five-dimensional metric f(R) gravity and the accelerated universe

The metric f(R) theories of gravity are generalized to five-dimensional spacetimes. By assuming a hypersurface-orthogonal Killing vector field representing the compact fifth dimension, the five-dimensional theories are reduced to their four-dimensional formalism. Then we study the cosmology of a special class of f(R) = alpha R-m models in a spatially flat Friedmann-Robertson-Walker spacetime. It is shown that the parameter m can be constrained to a certain range by the current observed deceleration parameter, and its lower bound corresponds to the Kaluza-Klein theory. It turns out that both expansion and contraction of the extra dimension may prescribe the smooth transition from the deceleration era to the acceleration era in the recent past as well as an accelerated scenario for the present Universe. Hence, five-dimensional f(R) gravity can naturally account for the present accelerated expansion of the Universe. Moreover, the models predict a transition from acceleration to deceleration in the future, followed by a cosmic recollapse within finite time. This differs from the prediction of the five-dimensional Brans-Dicke theory but is inconsistent with a recent prediction based on loop quantum cosmology.