(0, 2) Heterotic gauge couplings and their M-theory origin Original Research Article

We work out the relation between automorphic forms on SO(2 + s, 2, Z) and gauge one-loop corrections of heterotic K3 x T2 string compactifications for the cases s = 0, 1. We find that one-loop gauge corrections of any orbifold limit of K3 can always be expressed by their instanton numbers and generic automorphic forms. These functions classify also one-loop gauge thresholds of N = 1 (0, 2) heterotic compactifications based on toroidal orbifolds T6Zν. We compare these results with the gauge couplings of M-theory compactified on S1Z2 × T6Zν using Witteʹs Calabi-Yau strong coupling expansion.