Twisted conjugacy classes in Lie groups

TL;DR

This paper investigates conditions under which twisted conjugacy classes in Lie groups have infinite Reidemeister numbers, establishing the topological $R_ fty$-property for various classes of Lie groups.

Contribution

It provides necessary and sufficient conditions for infinite Reidemeister numbers in Lie groups and identifies classes with the topological $R_ fty$-property.

Findings

Connected non-nilpotent Lie groups have infinite Reidemeister numbers for some automorphisms.

Certain solvable Lie groups, including upper triangular matrices, have the topological $R_ fty$-property.

SL(2,R) and GL(2,R) also exhibit the topological $R_ fty$-property.

Abstract

We consider twisted conjugacy classes of continuous automorphisms $\varphi$ of a Lie group $G$. We obtain a necessary and sufficient condition on $\varphi$ for its Reidemeister number, the number of twisted conjugacy classes, to be infinite when $G$ is connected and solvable or compactly generated and nilpotent. We also show for a general connected Lie group $G$ that the number of conjugacy classes is infinite. We prove that for a connected non-nilpotent Lie group $G$, there exists $n\in \mathbb{N}$ such that Reidemeister number of $\varphi^n$ is infinite for every $\varphi$. We say that $G$ has topological $R_\infty$-property if the Reidemeister number of every $\varphi$ is infinite. We obtain conditions on a connected solvable Lie group under which it has topological $R_\infty$-property; which, in particular, enables us to prove that the group of invertible $n\times n$ upper triangular real matrices and its quotient group modulo its center have topological $R_\infty$-property for every $n\geq 2$. We also prove that the Walnut group also has this property. We show that ${\mathrm{SL}}(2,\mathbb{R})$ and ${\mathrm{GL}}(2,\mathbb{R})$ have topological $R_\infty$-property, and construct many examples of Lie groups with this property.