Counting the number of $\mathbb{Z}_{p}$-and $\mathbb{F}_{p}[t]$-fixed points of a discrete dynamical system with applications from arithmetic statistics, III (2505.24565v1)

Abstract: In this follow-up paper, we again inspect a surprising relationship between the set of fixed points of a polynomial map $\varphi_{d, c}$ defined by $\varphi_{d, c}(z) = z^d + c$ for all $c, z \in \mathcal{O}{K}$ or $c, z \in \mathbb{Z}{p}$ or $c, z \in \mathbb{F}{p}[t]$ and the coefficient $c$, where $K$ is any number field (not necessarily real) of degree $n > 1$, $p>2$ is any prime integer, and $d>2$ is an integer. As in \cite{BK1,BK2} we again wish to study here counting problems that are inspired by exhilarating advances in arithmetic statistics, and also partly by point-counting results of Narkiewicz on totally complex $K$-periodic points and of Adam-Fares on $\mathbb{Q}{p}$-periodic points (orbits) in arithmetic dynamics. In doing so, we then first prove that for any given prime $p\geq 3$ and any $\ell \in \mathbb{Z}^{+}$, the average number of distinct fixed points of any $\varphi_{p^{\ell}, c}$ modulo prime ideal $p\mathcal{O}{K}$ (modulo $p\mathbb{Z}{p}$) is bounded (if $\ell \in \mathbb{Z}^{+}\setminus{1, p}$) or zero or unbounded (if $\ell \in {1, p}$) as $c\to \infty$. Motivated further by an $\mathbb{F}{p}(t)$-periodic point-counting result of Benedetto, we also find that the average number in $\mathbb{F}{p}[t]$-setting behaves in the same way as in $\mathcal{O}_{K}$-setting. Finally, we then apply counting and statistical results from arithmetic statistics to immediately deduce here several counting and statistical results.