Feynman diagrams, ribbon graphs, and topological recursion of Eynard-Orantin

Abstract

We consider two seemingly unrelated problems, calculation of the WKB expansion of the harmonic oscillator wave functions and counting the number of Feynman diagrams in QED or in many-body physics and show that their solutions are both encoded in a single enumerative problem: calculation of the number of certain types of ribbon graphs. In turn, the numbers of such ribbon graphs as a function of the number of their vertices and edges can be determined recursively through the application of the topological recursion of Eynard-Orantin to the algebraic curve encoded in the Schrödinger equation of the harmonic oscillator. We show how the numbers of these ribbon graphs can be written down in closed form for any given number of vertices and edges. We use these numbers to obtain a formula for the number of N-rooted ribbon graphs with e edges, which is the same as the number of Feynman diagrams for 2N-point function with e + 1 − N loops.