Gorenstein homological dimension of group extensions

Abstract

We study the Gorenstein homological dimension $Ghd_k G$ of groups $G$ which are of type $FP_{\infty}$ over a commutative ring $k$. Our main result shows that, over an arbitrary ring $R$, every finitely presented Gorenstein flat $R$-module is projectively coresolved Gorenstein flat. Consequently, for a group $G$ of type $FP_\infty$ over $k$ with sfli$k<\infty$, the three natural dimensions for $G$, namely Gorenstein homological, Gorenstein cohomological and projectively coresolved Gorenstein flat, all coincide. Building on this collapse, we establish a Gorenstein homological analogue of Fel$'$dman's theorem, a formula for iterated $m$-fold self-extensions of a group $N$ of type $FP_\infty$ over $\mathbb Z$, and a field-detection theorem, showing that the Gorenstein homological dimension of a group of type $FP_\infty$ over a principal ideal domain is realized after passing to a suitable field.