Distal Actions of Automorphisms of Lie Groups $G$ on $\mathrm{Su}{\mathrm{b}}_{\mathrm{G}}$

Abstract

For a locally compact metrizable group $G$, we study the action of $\mathrm{Aut}(\mathrm{G})$ on $\mathrm{Su}{\mathrm{b}}_{\mathrm{G}}$, the set of closed subgroups of $G$ endowed with the Chabauty topology. Given an automorphism $T$ of $G$, we relate the distality of the $T$-action on $\mathrm{Su}{\mathrm{b}}_{\mathrm{G}}$ with that of the $T$-action on $G$ under a certain condition. If $G$ is a connected Lie group, we characterise the distality of the $T$-action on $\mathrm{Su}{\mathrm{b}}_{\mathrm{G}}$ in terms of compactness of the closed group generated by $T$ in $\mathrm{Aut}(\mathrm{G})$ under certain conditions on the center of $G$ or on $T$ as follows: $G$ has no compact central subgroup of positive dimension or $T$ is unipotent or $T$ is contained in the connected component of the identity in $\mathrm{Aut}(\mathrm{G})$. Moreover, we also show that a connected Lie group $G$ acts distally on $\mathrm{Su}{\mathrm{b}}_{\mathrm{G}}$ if and only if $G$ is either compact or it is isomorphic to a direct product of a compact group and a vector group. All the results on the Lie groups mentioned above hold for the action on $\mathrm{Su}{\mathrm{b}}_{\mathrm{G}}^{\mathrm{a}}$, a subset of $\mathrm{Su}{\mathrm{b}}_{\mathrm{G}}$ consisting of closed abelian subgroups of $G$.