On the rationality of the Nielsen zeta function for maps on solvmanifolds

In [3,9], the Nielsen zeta function $N_f(z)$ has been shown to be rational if $f$ is a self-map of an infra-solvmanifold of type (R). It is, however, still unknown whether $N_f(z)$ is rational for self-maps on solvmanifolds. In this paper, we prove that $N_f(z)$ is rational if $f$ is a self-map of a (compact) solvmanifold of dimension $\leq 5$. In any dimension, we show additionally that $N_f(z)$ is rational if $f$ is a self-map of an ${\cal NR}$-solvmanifold or a solvmanifold with fundamental group of the form ${\mathbb Z}^n\rtimes{\mathbb Z}$.