Sigma invariants for partial orders on nilpotent groups

Abstract

We prove that a map onto a nilpotent group $Q$ has finitely generated kernel if and only if the preimage of the positive cone is coarsely connected as a subset of the Cayley graph for every full archimedean partial order on $Q$. In case $Q$ is abelian, we recover the classical theorem that $N$ is finitely generated if and only if $S(G,N)\subseteq {\Sigma }^1(G)$. Furthermore, we provide a way to construct all such orders on nilpotent groups. A key step is to translate the classical setting based on characters into a language of orders on $G$.

21 pages, comments welcome