nLab Drinfel'd double




The Drinfel’d double- or quantum double-construction a sends a Hopf algebra to a quasi-triangular Hopf algebra [Drinfeld (1987)]; or more generally, it sends a quasi-Hopf algebra to a quasi-triangulated quasi-Hopf algebra [Majid (1994)].

Geometrically, if the given Hopf algebra is the group algebra of a finite group GG, then the quantum double is the groupoid convolution algebra of the corresponding inertia groupoid BGG adG\mathcal{L}\mathbf{B}G \simeq G \sslash_{ad} G (this is made almost explicit in Dijkgraaf, Pasquier & Roche (1990), eq. 2.1.10; the categorified version of this statement is highlighted in Hinich (2007)).

More generally, if the given quasi-Hopf algebra is the twisted groupoid convolution algebra of a group cohomology 3-cocycle c:BGB 3U(1)c \colon \mathbf{B}G \to \mathbf{B}^3 U(1), then the corresponding quantum double is the twisted groupoid convolution algebra of the inertia groupoid equipped with the transgressed 2-cocycle [Willerton (2005)]


Given a field kk, Drinfel’d (or Drinfeld or quantum) double of a finite dimensional Hopf kk-algebra HH is the tensor product algebra D(H)=HH *D(H) = H\otimes H^* where H *=Hom k(H,k)H^* = Hom_k(H, k) with induced canonical Hopf algebra structure. It appears that the canonical element in D(H)D(H) (the image of the identity under the isomorphism Hom k(H,H)HH *Hom_k(H,H) \cong H\otimes H^*) is a universal RR-element in D(H)D(H) making it into a quasitriangular Hopf algebra, which is making it “almost cocommutative”.

This quasitriangular structure in some infinite-dimensional versions of the construction is related to the quasitriangular structure on some quantum groups.


Relation to Yetter-Drinfeld modules

The category of modules over a quantum double of a finite-dimensional Hopf algebra HH is equivalent to the category of Yetter-Drinfeld modules of HH.

Relation to Drinfeld center

For HH a Hopf algebra arising as the groupoid convolution algebra of a finite groupoid, the category of modules of its Drinfeld double is equivalently the Drinfeld center of the category of modules of the original algebra.

More generally, the analog of this statement holds for orbifolds (Hinich (2007)).

Tannaka duality for categories of modules over monoids/associative algebras

monoid/associative algebracategory of modules
AAMod AMod_A
RR-algebraMod RMod_R-2-module
sesquialgebra2-ring = monoidal presentable category with colimit-preserving tensor product
bialgebrastrict 2-ring: monoidal category with fiber functor
Hopf algebrarigid monoidal category with fiber functor
hopfish algebra (correct version)rigid monoidal category (without fiber functor)
weak Hopf algebrafusion category with generalized fiber functor
quasitriangular bialgebrabraided monoidal category with fiber functor
triangular bialgebrasymmetric monoidal category with fiber functor
quasitriangular Hopf algebra (quantum group)rigid braided monoidal category with fiber functor
triangular Hopf algebrarigid symmetric monoidal category with fiber functor
supercommutative Hopf algebra (supergroup)rigid symmetric monoidal category with fiber functor and Schur smallness
form Drinfeld doubleform Drinfeld center
trialgebraHopf monoidal category

2-Tannaka duality for module categories over monoidal categories

monoidal category2-category of module categories
AAMod AMod_A
RR-2-algebraMod RMod_R-3-module
Hopf monoidal categorymonoidal 2-category (with some duality and strictness structure)

3-Tannaka duality for module 2-categories over monoidal 2-categories

monoidal 2-category3-category of module 2-categories
AAMod AMod_A
RR-3-algebraMod RMod_R-4-module


The original articles:


The generalization of the double construction to quasi-Hopf algebras motivated by

which is reviewed in

  • A. Coste, J-M. Maillard, Representation Theory of Twisted Group Double, Annales Fond.Broglie 29 (2004) 681-694, (arXiv:hep-th/0309257)

was obtained in

Interpretation via transgression in group cohomology:

The special case of the Drinfeld double of a finite group is discussed further in

  • Hui-Xiang Chen, Gerhard Hiss, Notes on the Drinfeld double of a finite-dimensional group algebra (pdf)

A characterization of the (quasi-)Hopf algebras arising this way is in

  • Sonia Natale, On group theoretical Hopf algebras and exact factorization of finite groups (arXiv:math/0208054)

The equivalence of category of modules over the Drinfeld double for the case of orbifolds, hence representations of the inertia orbifold, with the Drinfeld center of the category of representations of the original orbifold is discussed in

Last revised on September 14, 2023 at 10:44:02. See the history of this page for a list of all contributions to it.