Right-angled Artin groups and the cohomology basis graph

Abstract

Let $\Gamma$ be a finite graph and let $A(\Gamma )$ be the corresponding right-angled Artin group. From an arbitrary basis $\mathcal{B}$ of $H^1(A(\Gamma ),\mathbb{F})$ over an arbitrary field, we construct a natural graph ${\Gamma }_{\mathcal{B}}$ from the cup product, called the \emph{cohomology basis graph}. We show that ${\Gamma }_{\mathcal{B}}$ always contains $\Gamma$ as a subgraph. This provides an effective way to reconstruct the defining graph $\Gamma$ from the cohomology of $A(\Gamma )$, to characterize the planarity of the defining graph from the algebra of $A(\Gamma )$, and to recover many other natural graph-theoretic invariants. We also investigate the behavior of the cohomology basis graph under passage to elementary subminors, and show that it is not well-behaved under edge contraction.

18 pages, to appear in Proc. Edinburgh Math. Soc