Nicolai, Hermann Quantum Gravity & Unified Theories, AEI-Golm, MPI for Gravitational Physics, Max Planck Society;
328671.pdf (Publisher version), 209KB
Gebert, R. W., & Nicolai, H. (1997). An affine string vertex operator construction at an arbitrary level. Journal of Mathematical Physics, 38(9), 4435-4450. doi:10.1063/1.532135.