SPECTRAL FLOW AND FREE FIELD REALIZATIONS OF BOSONIC STRINGS ON NAPPI-WITTEN GROUP MANIFOLD

In this paper we study some aspects of closed string theories in the Nappi-Witten space-time. The effects of spectral flow on the geodesics are studied in terms of an explicit parametrization of the group manifold. The worldsheets of the closed strings under the spectral flow of the geodesics can be classified into four classes, each with a geometric interpretation. We also obtain a free field realization of the Nappi-Witten affine Lie algebra in the most general conditions using a different but equivalent parametrization of the group manifold.