UNITARITY OF RATIONAL N=2 SUPERCONFORMAL THEORIES

We demonstrate that all rational models of the N = 2 super Virasoro al gebra are unitary. Our arguments are based on three different methods: we determine Zhu's algebra A(H-0) (for which we give a physically mot ivated derivation) explicitly for certain theories, we analyse the mod ular properties of some of the vacuum characters, and we use the coset realisation of the algebra in terms of su(2) and two free fermions. S ome of our arguments generalise to the Kazama-Suzuki models indicating that all rational N = 2 supersymmetric models might be unitary.