Graphs on surfaces and khovanov homology

Abstract

Oriented ribbon graphs (dessins d'enfant) are graphs embedded in oriented surfaces. A quasi tree of a ribbon graph is a spanning subgraph with one face, which is described by an ordered chord diagram. We show that for any link diagram L, there is an associated ribbon graph whose quasi trees correspond bijectively to spanning trees of the graph obtained by checkerboard coloring L. This correspondence preserves the bigrading used for the spanning tree model of Khovanov homology, whose Euler characteristic is the Jones polynomial of L. Thus, Khovanov homology can be expressed in terms of ribbon graphs, with generators given by ordered chord diagrams. © 2007 Mathematical Sciences Publishers.