Algebraic dynamics of skew-linear self-maps

Abstract

Let $X$ be a variety defined over an algebraically closed field $k$ of characteristic $0$, let $N\in \mathbb{N}$, let $g:X⇢X$ be a dominant rational self-map, and let $A:{\mathbb{A}}^N\to {\mathbb{A}}^N$ be a linear transformation defined over $k(X)$, i.e., for a Zariski open dense subset $U\subset X$, we have that for $x\in U(k)$, the specialization $A(x)$ is an $N$-by-$N$ matrix with entries in $k$. We let $f:X\times {\mathbb{A}}^N⇢X\times {\mathbb{A}}^N$ be the rational endomorphism given by $(x,y)\mapsto (g(x),A(x)y)$. We prove that if the determinant of $A$ is nonzero and if there exists $x\in X(k)$ such that its orbit ${\mathcal{O}}_g(x)$ is Zariski dense in $X$, then either there exists a point $z\in (X\times {\mathbb{A}}^N)(k)$ such that its orbit ${\mathcal{O}}_f(z)$ is Zariski dense in $X\times {\mathbb{A}}^N$ or there exists a nonconstant rational function $\psi \in k(X\times {\mathbb{A}}^N)$ such that $\psi \circ f=\psi$. Our result provides additional evidence to a conjecture of Medvedev and Scanlon.

To appear in Proceedings of the AMS