A conjecture strengthening the Zariski dense orbit problem for birational maps of dynamical degree one

Abstract

We formulate a strengthening of the Zariski dense orbit conjecture for birational maps of dynamical degree one. So, given a quasiprojective variety $X$ defined over an algebraically closed field $K$ of characteristic $0$, endowed with a birational self-map $\ddot{I}•$ of dynamical degree $1$, we expect that either there exists a non-constant rational function $f:X⇢{\mathbb{P}}^1$ such that $f\circ \ddot{I}•=f$, or there exists a proper subvariety $Y\subset X$ with the property that for any invariant proper subvariety $Z\subset X$, we have that $Z\subseteq Y$. We prove our conjecture for automorphisms $\ddot{I}•$ of dynamical degree $1$ of semiabelian varieties $X$. Also, we prove a related result for regular dominant self-maps $\ddot{I}•$ of semiabelian varieties $X$: assuming $\ddot{I}•$ does not preserve a non-constant rational function, we have that the dynamical degree of $\ddot{I}•$ is larger than $1$ if and only if the union of all $\ddot{I}•$-invariant proper subvarieties of $X$ is Zariski dense. We give applications of our results to representation theoretic questions about twisted homogeneous coordinate rings associated to abelian varieties.

13 pages