Reidemeister classes in some wreath products by $\mathbb Z^k$

Mikhail I. Fraiman, Evgenij V. Troitsky

Published 2022-07-09Version 1

Among restricted wreath products $G\wr \mathbb Z^k $, where $G$ is a finite Abelian group, we find three large classes of groups admitting an automorphism $\varphi$ with finite Reidemeister number $R(\varphi)$ (number of $\varphi$-twisted conjugacy classes). In other words, groups from these classes do not have the $R_\infty$ property. If a general automorphism $\varphi$ of $G\wr \mathbb Z^k$ has a finite order (this is the case for $\varphi$ detected in the first part of the paper) and $R(\varphi)<\infty$, we prove that $R(\varphi)$ coincides with the number of equivalence classes of finite-dimensional irreducible unitary representations of $G\wr \mathbb Z^k$, which are fixed by the dual map $[\rho]\mapsto [\rho\circ \varphi]$ (i.e. we prove the conjecture about finite twisted Burnside-Frobenius theorem, TBFT$_f$, for these $\varphi$).