Low-dimensional G-bordism and G-modular TQFTs
Kevin Walker (Microsoft Research Station Q)
Let G denote a class of manifolds (such as SO (oriented), O (unoriented), Spin, Pin+, Pin-, manifolds with spin defects). We define a 2+1-dimensional G-modular TQFT to be one which lives on the boundary of a bordism-invariant 3+1-dimensional G-TQFT. Correspondingly, we define a G-modular braided category to be a G-premodular category which leads to a bordism-invariant 3+1-dimensional TQFT. When G = SO, this reproduces the familiar Witten-Reshetikhin-Turaev TQFTs and corresponding modular tensor categories. For other examples of G, non-zero G-bordism groups in dimensions 4 or lower lead to interesting complications (anomalies, mapping class group extensions, obstructions to defining the G-modular theory on all G-manifolds).