Abstract:
String theory on a d-dimensional torus features an O(d,d) duality symmetry. It has been suggested that the low-energy effective action can be formulated with a larger O(D,D) symmetry (D=10 or 26), even before putting the theory on a torus. This approach, which goes by the name of Double Field Theory (DFT), has proven very useful. I will address the problem of constructing higher derivative invariants in this formalism. In agreement with the literature we find that a quadratic Riemann invariant can be constructed, which can account for the first alpha'-correction to the bosonic and heterotic string. However, we find that no cubic or quartic Riemann invariants can be constructed. This suggests that the quartic Riemann terms arising at order alpha'^3 in string theory do not have a DFT embedding.