The many faces of Ocneanu cells

We define generalised chiral vertex operators covariant under the Ocneanu double triangle algebra A, a novel quantum symmetry intrinsic to a given rational 2d conformal field theory. This provides a chiral approach, which, unlike the conventional one, makes explicit various algebraic structures encountered previously in the study of these theories and of the associated critical lattice models, and thus allows their unified treatment. The triangular Ocneanu cells, the 3j-symbols of the weak Hopf algebra A, reappear in several guises. With A and its dual algebra (A) over cap one associates a pair of graphs, G and (G) over tilde. While G are known to encode complete sets of conformal boundary states, the Ocneanu graphs (G) over tilde classify twisted torus partition functions. The fusion algebra of the twist operators provides the data determining (A) over cap. The study of bulk field correlators in the presence of twists reveals that the Ocneanu graph quantum symmetry gives also an information on the field operator algebra. (C) 2001 Elsevier Science B.V. All rights reserved.