CATEGORICAL CENTERS AND RESHETIKHIN-TURAEV INVARIANTS
ALAIN BRUGUIÈRES, ALEXIS VIRELIZIER
Abstract
A theorem of Müger asserts that the center of a spherical 𝕜-linear category is a modular category if 𝕜 is an algebraically closed field and the dimension of is invertible. We generalize this result to the case where 𝕜 is an arbitrary commutative ring, without restriction on the dimension of the category. Moreover we construct the analogue of the Reshetikhin-Turaev invariant associated to and give an algorithm for computing this invariant in terms of certain explicit morphisms in the category . Our approach is based on (a) Lyubashenko’s construction of the Reshetikhin-Turaev invariant in terms of the coend of a ribbon category; (b) an explicit algorithm for computing this invariant via Hopf diagrams; (c) an algebraic interpretation of the center of as the category of modules over a certain Hopf monad Z on the category ; (d) a generalization of the classical notion of Drinfeld double to Hopf monads, which, applied to the Hopf monad Z, provides an explicit description of the coend of in terms of the category .