Reidemeister classes, wreath products and solvability

TL;DR

This paper investigates Reidemeister classes in wreath products involving finite groups and integer lattices, proving a conjecture relating automorphisms with finite Reidemeister number to the group's solvability.

Contribution

It proves the TBFT_f conjecture for certain wreath products and establishes that groups with automorphisms of finite Reidemeister number are solvable-by-finite.

Findings

Reidemeister number corresponds to fixed points of dual automorphism

TBFT_f conjecture is proved for specific wreath products

Automorphisms with finite Reidemeister number imply the group is solvable-by-finite

Abstract

Reidemeister (or twisted conjugacy) classes are considered in restricted wreath products of the form $G\wr \mathbb{Z}^k$, where $G$ is a finite group. For an automorphism $\varphi$ of finite order (supposed to be the same for the torsion subgroup $\oplus G$ and the quotient $\mathbb{Z}^k$) with finite number $R(\varphi)$ of Reidemeister classes, this number is identified with the number of equivalence classes of finite-dimensional unitary irreducible representations of the product that are fixed by the dual homeomorphism $\widehat{\varphi}$ (i.e. the so-called conjecture TBFT$_f$ is proved in this case). For these groups and automorphisms, we prove the following conjecture: if a finitely generated residually finite group has an automorphism with $R(\varphi)<\infty$ then it is solvable-by-finite (so-called conjecture R).