Formula omitted]-action for ribbon quasi-Hopf algebras

Abstract

We study the universal Hopf algebra L of Majid and Lyubashenko in the case that the underlying ribbon category is the category of representations of a finite dimensional ribbon quasi-Hopf algebra A. We show that L=A⁎ with coadjoint action and compute the Hopf algebra structure morphisms of L in terms of the defining data of A. We give explicitly the condition on A which makes Rep A factorisable and compute Lyubashenko's projective SL(2,Z)-action on the centre of A in this case.The point of this exercise is to provide the groundwork for the applications to ribbon categories arising in logarithmic conformal field theories – in particular symplectic fermions and Wp-models – and to test a conjectural non-semisimple Verlinde formula.