Algebraic and measurable embeddings between square-free right-angled Artin groups

Abstract

Let $Γ,Δ$ be finite simplicial graphs, and assume that $Γ$ has no induced squares. We prove that the right-angled Artin group $A(Δ)$ measurably embeds into $A(Γ)$ if and only if $A(Δ)$ embeds as a subgroup in a graph product of free abelian groups over $Γ$. This in turn has a graph-theoretical characterisation which can be checked algorithmically. If additionally $A(Γ)$ and $A(Δ)$ have cohomological dimension equal to two and $A(Γ)$ is not isomorphic to $\mathbb{Z}\times F_n$, we get that $A(Δ)$ measurably embeds into $A(Γ)$ if and only if it embeds as a subgroup in $A(Γ)$. Our proof relies on the following algebraic statement. Let $K_1,\dots,K_n$ be a family of pairwise disjoint cliques in the square-free graph $Γ$ (or more generally in its extension graph $Γ^{\mathrm{ext}}$), and let $g_1,\dots,g_n$ be elements of $A(Γ)$ with respective parabolic supports $A(K_1),\dots,A(K_n)$. Then the subgroup of $A(Γ)$ generated by $g_1,\dots,g_n$ is a right-angled Artin group, where the only relations impose that $g_i$ and $g_j$ commute if $K_i\cup K_j$ is contained in a clique of $Γ$ (or of $Γ^{\mathrm{ext}}$).