Algebraic dynamics of skew-linear self-maps

TL;DR

This paper studies the dynamics of skew-linear maps on algebraic varieties, proving conditions under which orbits are dense or rational functions are invariant, supporting a conjecture in algebraic dynamics.

Contribution

It establishes criteria for Zariski dense orbits or invariant rational functions for skew-linear self-maps, extending understanding in algebraic dynamics.

Findings

If the determinant of A is nonzero and a point with dense orbit exists, then either a dense orbit exists in the product space or an invariant rational function exists.

The result supports the Medvedev-Scanlon conjecture in the context of skew-linear maps.

Provides conditions linking orbit density and invariant functions in algebraic dynamics.

Abstract

Let $X$ be a variety defined over an algebraically closed field $k$ of characteristic $0$, let $N\in\mathbb{N}$, let $g:X\dashrightarrow X$ 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 $f:X\times\mathbb{A}^N\dashrightarrow X\times \mathbb{A}^N$ 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.