Twisted vertex operators and representations of finite Heisenberg groups

This paper discusses the construction of simply-laced affine algebras twisted Vertex operators. Special care is given to the explicit determination of the zero-mode part of the vertices. The result can be neatly formulated in terms of finite Heisenberg groups, thereby reflecting the underlying quantization problem for the motion of the center-of-mass of the string, which takes place in a nonconnected manifold