A categorification of Quinn's finite total homotopy TQFT with application to TQFTs and once-extended TQFTs derived from strict omega-groupoids

Abstract

We first revisit the construction of Quinn's finite total homotopy TQFT, which depends on the choice of a homotopy finite space, $\boldsymbol{B}$. This constitutes a vast generalisation of the Dijkgraaf-Witten TQFT, with a trivial cocycle, and of Yetter's homotopy 2-type TQFT. We build our construction directly from homotopy theoretical techniques, and hence, as in Quinn's original notes from 1995, the construction works in all dimensions. Our aim in this is to provide background for giving in detail the construction of a once-extended TQFT categorifying Quinn's finite total homotopy TQFT, in the form of a symmetric monoidal bifunctor from the bicategory of manifolds, cobordisms and extended cobordisms, first to the symmetric monoidal bicategory of profunctors (enriched over vector spaces), and then to the Morita bicategory of algebras, bimodules and bimodule maps. These once-extended versions of Quinn's finite total homotopy TQFT likewise are defined for all dimensions, and, as with the original version, depend on the choice of a homotopy finite space, $\boldsymbol{B}$. To show the utility of this approach, we explicitly compute both Quinn's finite total homotopy TQFT, and its extended version, for the case when $\boldsymbol{B}$ is the classifying space of a homotopy finite omega-groupoid, in this paper taking the form of a crossed complex, following Brown and Higgins. The constructions in this paper include, in particular, the description of once-extended TQFTs derived from the classifying space of a finite strict 2-group, of relevance for modelling discrete higher gauge theory, although the techniques involved are considerably more general.