GAUGE-SYMMETRY ENHANCEMENT AND N=2 SUPERSYMMETRIC QUANTUM BLACK-HOLESIN 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 conside red. First, these quantum black holes are investigated at generic poin ts in moduli space. Then ''linearized'' non-abelian black holes are in vestigated representing a subset of non-abelian black hole solutions a t critical points of perturbative gauge symmetry enhancement in moduli space. It is shown that the entropy of ''linearized'' non-abelian bla ck holes can be obtained, starting at non-critical points in moduli sp ace, by continuous variation of the moduli and a proper identification of the non-abelian charges. (C) 1998 Elsevier Science B.V.