Positive Lin-Lu-Yau curvature, planar graphs, and forbidden minors

Abstract: Over the past few decades, several notions of graph curvature have been introduced. Among them, Ollivier curvature, defined through optimal transport, and its Lin--Lu--Yau variant provide notions of curvature for graphs which retain several features of their counterpart in Riemannian geometry. A classical problem in this context is to understand the global structure of positively curved spaces. Lu and Wang proved that there are only finitely many positively curved planar graphs of minimum degree at least 3. In this paper, we study two directions motivated by this result. We first show that for fixed $2\leq s\leq t$, there are only finitely many positively curved $K_{s,t}$-minor-free graphs with minimum degree at least $s$. In particular, this generalizes the result of Lu and Wang to graphs embeddable on any fixed surface. We then give a complete classification of positively curved 5-connected plane triangulations. In particular, we show that there are only five examples, on 12, 14, 15, 16, and 17 vertices.