We give a characterization of extremal irreducible discrete subfactors (N ⊆ M, E) where N is type II 1 in terms of connected W*-algebra objects in rigid C*-tensor categories. We prove an equivalence of categories where the morphisms for discrete inclusions are normal N − N bilinear ucp maps which preserve the state τ • E, and the morphisms for W*-algebra objects are categorical ucp morphisms.As an application, we get a well-behaved notion of the standard invariant of an extremal irreducible discrete subfactor, together with a subfactor reconstruction theorem. Thus our equivalence provides many new examples of discrete inclusions (N ⊆ M, E), in particular, examples where M is type III coming from non Kac-type discrete quantum groups and associated module W*-categories. Finally, we obtain a Galois correspondence between intermediate subfactors of an extremal irreducible discrete inclusion and intermediate W*-algebra objects. Corollary B. The realization |A| H of the connected W*-algebra object A coming from a discrete quantum group G = (C, F) together with a fully faithful representation H : C → Bim sp bf (N ) is type III if and only if G is not Kac-type. (See Section 6.3 for more details.) This corollary is related to [Vae05, Thm. 3.5] in the case of compact quantum groups. De Commer and Yamashita's classification of T LJ (δ)-module W*-categories [DCY15] gives many more such examples (see Section 6.4 for more details).
BackgroundWe refer the reader to [HP17b, §2.1-2.2] and [JP17a, §2.1-2.3] for background on rigid C*tensor categories. Of particular importance is their bi-involutive structure, consisting of two commuting involutions (the adjoint * and conjugate · ) together with coherence data. As usual, we will suppress all associators, unitors, and the involutive structure morphisms.We fix a rigid C*-tensor category C. As in [JP17a, §2.4], Vec(C) denotes the involutive tensor category of linear functors C op → Vec with linear transformations. Note that Vec(C) = ind(C ), where C denotes the involutive tensor category obtained from C by forgetting the adjoint. As in [JP17a, §2.6], Hilb(C) denotes the bi-involutive tensor W*-category of linear dagger functors C op → Hilb with bounded natural transformations. Note that Hilb(C) is the Neshveyev-Yamashita unitary ind-category of C from [NY16].
6Proposition 5.42. The map κ gives a natural isomorphism id ⇒ | · | H .