Fully extended $r$-spin TQFTs

Abstract

We prove the $r$-spin cobordism hypothesis in the setting of (weak) 2-categories for every positive integer $r$: the 2-groupoid of 2-dimensional fully extended $r$-spin TQFTs with given target is equivalent to the homotopy fixed points of an induced ${\mathrm{Spin}}_2^r$-action. In particular, such TQFTs are classified by fully dualisable objects together with a trivialisation of the $r$th power of their Serre automorphisms. For $r=1$, we recover the oriented case (on which our proof builds), while ordinary spin structures correspond to $r=2$.

To construct examples, we explicitly describe ${\mathrm{Spin}}_2^r$-homotopy fixed points in the equivariant completion of any symmetric monoidal 2-category. We also show that every object in a 2-category of Landau–Ginzburg models gives rise to fully extended spin TQFTs and that half of these do not factor through the oriented bordism 2-category.