Theisen, Stefan Quantum Gravity & Unified Theories, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;
NuclPhyB325-1989.pdf (Publisher version), 2MB
Ferrara, S., Lüst, D., & Theisen, S. (1990). World-sheet versus spectrum symmetries in heterotic and type II superstrings. Nuclear Physics B, 325(2), 501-525. doi:10.1016/0550-3213(89)90464-1.