The Cohomology of Pro-$p$-Groups with Group Ring Coefficients and Virtual Poincare Duality

The relationship between the group-theoretic properties of a pro-$p$-group $G$ and the $G$-module structure of the group $H^n(G,\mathbb F_q[[G]])$ is studied. A necessary and sufficient condition for a pro-$p$-group $G$ to contain an open Poincare subgroup of dimension $n$ is obtained. This condition does not require that $G$ have finite cohomological dimension and, therefore, applies to groups with torsion. Results concerning the possible values of $\dim_{\mathbb F_p}H^n(G,\mathbb F_p[[G]])$ are also obtained.