On subdirect products of type $FP_n$ of limit groups over Droms RAAGs

TL;DR

This paper extends known results about limit groups over free groups to those over Droms RAAGs, establishing structural properties, subgroup projections, and homological growth, including $L^2$-Betti numbers.

Contribution

It introduces the class of limit groups over Droms RAAGs, proves they are free-by-(torsion-free nilpotent), and analyzes their subgroup and homological properties.

Findings

Limit groups over Droms RAAGs are free-by-(torsion-free nilpotent).

Full subdirect products of these groups have finite index projections.

Homology growth and $L^2$-Betti numbers are computed in various dimensions.

Abstract

We generalize some known results for limit groups over free groups and residually free groups to limit groups over Droms RAAGs and residually Droms RAAGs, respectively. We show that limit groups over Droms RAAGs are free-by-(torsion-free nilpotent). We prove that if $S$ is a full subdirect product of type $FP_s(\mathbb{Q})$ of limit groups over Droms RAAGs with trivial center, then the projection of $S$ to the direct product of any $s$ of the limit groups over Droms RAAGs has finite index. Moreover, we compute the growth of homology groups and the volume gradients for limit groups over Droms RAAGs in any dimension and for finitely presented residually Droms RAAGs of type $FP_m$ in dimensions up to $m$. In particular, this gives the values of the analytic $L^2$-Betti numbers of these groups in the respective dimensions.