We incorporate a category considered by Kazhdan and Lusztig of certain modules (of a fixed level ℓ, not a positive integer) for an affine Lie algebra, into the representation theory of vertex operator algebras. We do this using the logarithmic tensor product theory for generalized modules for a vertex operator algebra developed by Huang, Lepowsky and the author; we prove that the conditions for applying this general logarithmic tensor product theory hold. As a consequence, we prove that this category has a natural vertex tensor category structure, and in particular we obtain a new, vertex-algebraic, construction of the natural associativity isomorphisms and proof of their properties.

Partial support from NSF grant DMS-0070800 is gratefully acknowledged.