Post-Newtonian expansion for Gauss-Bonnet Gravity

The observed late time accelerated expansion of the universe [1] combined with the problems that arise when trying to rationalize it with the simplest of explanations, such as a cosmological constant [2], have triggered an increased interest in finding alternatives for the nature of dark energy. Scalar fields, widely used in the inflationary paradigm [3], constitute a familiar way of providing accelerated expansion. Scalartensor theory is therefore an appealing candidate as an alternative theory of gravity that can provide the desired cosmological dynamics [4]. However, there are motivations from String theory to believe that scalar fields might not be coupled to the Ricci scalar, as in scalar-tensor theory, but to the Gauss-Bonnet term,