Bounded-degree planar graphs do not have bounded-degree product structure

Vida Dujmović¹ ; Gwenaël Joret² ; Piotr Micek³ ; Pat Morin⁴ ; David Wood⁵

¹University of Ottawa
²Université Libre de Bruxelles
³Jagiellonian University
⁴Carleton University
⁵Monash University

The electronic journal of combinatorics, Tome 31 (2024) no. 2

Résumé

Product structure theorems are a collection of recent results that have been used to resolve a number of longstanding open problems on planar graphs and related graph classes. One particularly useful version states that every planar graph $G$ is contained in the strong product of a $3$-tree $H$, a path $P$, and a $3$-cycle $K_3$; written as $G\subseteq H\boxtimes P\boxtimes K_3$. A number of researchers have asked if this theorem can be strengthened so that the maximum degree in $H$ can be bounded by a function of the maximum degree in $G$. We show that no such strengthening is possible. Specifically, we describe an infinite family $\mathcal{G}$ of planar graphs of maximum degree $5$ such that, if an $n$-vertex member $G$ of $\mathcal{G}$ is isomorphic to a subgraph of $H\boxtimes P\boxtimes K_c$ where $P$ is a path and $H$ is a graph of maximum degree $\Delta$ and treewidth $t$, then $t\Delta c \ge 2^{\Omega(\sqrt{\log\log n})}$.

Détail

DOI : 10.37236/11712

Classification : 05C76, 05C10, 05C75
Mots-clés : planar graphs, product structure