Representation Theory of the Affine Lie Superalgebra at Fractional Level

N= 2 noncritical strings are closely related to the Wess-Zumino-Novikov-Witten model, and there is much hope to further probe the former by using the algebraic apparatus provided by the latter. An important ingredient is the precise knowledge of the representation theory at fractional level. In this paper, the embedding diagrams of singular vectors appearing in Verma modules for fractional values of the level (, p and q coprime) are derived analytically. The nilpotency of the fermionic generators in $hslc$ requires the introduction of a nontrivial generalisation of the MFF construction to relate singular vectors among themselves. The diagrams reveal a striking similarity with the degenerate representations of the N= 2 superconformal algebra. Received: 10 June 1996,/,Accepted: 8 October 1996