Threshold corrections in K3 × T2 heterotic string compactifications Original Research Article

We consider compactifications of the heterotic string on K3 × T2 so that the resulting theory in d = 4 space-time dimensions has N = 2 supersymmetry. The gravitational and gauge coupling constants of the low-energy effective theory receive threshold corrections from loops of superheavy string states. We calculate these corrections for the case when the K3 surface is a Zn orbifold of a four-torus T4. The results are used to determine the one-loop prepotential F0(1) for the vector multiplets and the gravitational coupling F1(1).