Exact solutions of heterotic string theory corresponding to four-dimensional charge $Q$ magnetic black holes are constructed as tensor products of an $\frac{\mathrm{SU}\mathrm{}\left(2\right)\mathrm{}}{Z(2Q+2)\mathrm{}}$ WZW orbifold with a (0,1) supersymmetric SU(1,1)/U(1) WZW coset model. The spectrum is analyzed in some detail. "Bad" marginal operators are found which are argued to deform these theories to asymptotically flat black holes. Surprising behavior is found for small values of $Q$, where low-energy field theory is inapplicable. At the minimal value $Q=1\mathrm{}$, the theory degenerates. Renormalization-group arguments are given that suggest the potential gravitational singularity of the low-energy field theory is resolved by a massive two-dimensional field theory. At $Q=0\mathrm{}$, a stable, neutral "remnant," of potential relevance to the black hole information paradox, is found.

• Received 9 June 1993

DOI:https://doi.org/10.1103/PhysRevD.48.5784