Heterotic sigma models on T 8 and the Borcherds automorphic form Φ12

Abstract

We consider the spectrum of BPS states of the heterotic sigma model with (0, 8) supersymmetry and T8 target, as well as its second-quantized counterpart. We show that the counting function for such states is intimately related to Borcherds’ automorphic form Φ12, a modular form which exhibits automorphy for O(2, 26; ℤ). We comment on possible implications for Umbral moonshine and theories of AdS3 gravity.