Tree independence number I. (Even hole, diamond, pyramid)-free graphs

Abstract

The tree-independence number $\text{tree-}\alpha$, first defined and studied by Dallard, Milanič, and Štorgel, is a variant of treewidth tailored to solving the maximum independent set problem. Over a series of papers, Abrishami et al. developed the so-called central bag method to study induced obstructions to bounded treewidth. Among others, they showed that, in a certain superclass $C$ of (even hole, diamond, pyramid)-free graphs, treewidth is bounded by a function of the clique number. In this paper, we relax the bounded clique number assumption, and show that $C$ has bounded $\text{tree-}\alpha$. Via existing results, this yields a polynomial-time algorithm for the Maximum Weight Independent Set problem in this class. Our result also corroborates, for this class of graphs, a conjecture of Dallard, Milanič, and Štorgel that in a hereditary graph class, $\text{tree-}\alpha$ is bounded if and only if the treewidth is bounded by a function of the clique number.