Dark energy and matter from a five-dimensional Chern-Simons cosmology

A Friedman-Robertson-Walker cosmology arising from a five-dimensional Chern-Simons (CS) theory for the group S0(1,5) coupled to matter is considered as an alternative model for dark energy and matter. The four-dimensional reduction describes an accelerating universe having a time dependent Newton's coupling G and a positive cosmological constant. Five dimensional matter gives rise to what we interprete as four dimensional ordinary plus dark matter and a dark energy is provided by a cosmological constant term plus a fluid arising from the CS coupling. The case of five dust is studied in detail, leading to acceptable limits for most of the cosmological parameters considered, in the context of an open non-flat universe. Nevertheless, a value for ${\dot G}/G$ which is two orders of magnitude higher than recent bounds is predicted.