Embedded surface invariants via the Broda-Petit construction

Abstract

We recall Petit's construction of "dichromatic" invariants of 4-manifolds computed from Kirby diagrams using a nested pair of ribbon fusion categories $ B \subset C $ as initial data. Along the way we prove a lemma that fits the use of formal linear combinations of simple objects with quantum dimensions a coefficients as in the constructions of Reshetikhin-Turaev, Broda, and Petit more firmly in the functorial framework favored by the authors. We then show that Hughes et al.'s banded-link presentations of surfaces embedded in 4-manifolds provide a means whereby Frobenius algebra in $B$ together with a suitable module over it lying in $C$, give rise to an invariant of a surface-4-manifold pair. We provide a class of examples of suitable initial data and compute sufficient examples to show the invariant is sensitive to both genus and knotting.