Almost TQFTs via colored ribbon graphs

Abstract

In this paper, we introduce ribbon TQFTs via Edge Contraction/Construction Axioms of colored ribbon graphs as an extension of the 2D TQFT axioms for ribbon graphs formulated in arXiv:1508.05922. We investigate nearly Frobenius structures and Almost TQFTs defined in arXiv:1907.05470 together with ribbon TQFTs. We give a classification result for ribbon TQFTs that extends the one obtained for Frobenius algebras in arXiv:1508.05922. In particular, the Edge Contraction/Construction Axioms of colored ribbon graphs in this work become equivalent to the functorial Axioms of TQFTs governed by the sewing principle of Atiyah and Segal discussed in arXiv:2510.03128 and arXiv:1907.05470. As an application, we obtain that the recursion of generalized Catalan numbers can be twisted by Almost TQFT for co-unital nearly Frobenius algebra.