Quantum Black Holes in Heterotic String Vacua

N = 2 supersymmetric quantum black holes in the heterotic S-T -U model are presented. In particular three classes of axion-free quantum black holes with half the N = 2, D = 4 supersymmetries unbroken are considered. First, these quantum black holes are investigated at generic points in moduli space. Then “linearized” non-abelian black holes are considered, which can occur at critical points of perturbative gauge symmetry enhancement in moduli space. In this context the connection between abelian and linearized non-abelian black holes in heterotic string vacua is explained. It is shown that the entropy of black holes at critical points of perturbative gauge symmetry enhancement can be reached, starting at non-critical points, by continuous variation of the moduli and a proper identification of the non-abelian charges.