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Acta Mathematica Vietnamica

CATEGORICAL CENTERS AND RESHETIKHIN-TURAEV INVARIANTS

ALAIN BRUGUIÈRES, ALEXIS VIRELIZIER

Abstract

A theorem of Müger asserts that the center Z(C) of a spherical k-linear category C is a modular category if k is an algebraically closed field and the dimension of C 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 Z(C) and give an algorithm for computing this invariant in terms of certain explicit morphisms in the category C. 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 C as the category of modules over a certain Hopf monad Z on the category C; (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 Z(C) in terms of the category C.