Integral points and orbits of endomorphisms on the projective plane

TL;DR

This paper investigates the density of integral points on affine surfaces in the projective plane, classifying cases by their logarithmic Kodaira dimension, and explores integral points in orbits under endomorphisms, linking to the Lang-Vojta conjecture.

Contribution

It provides a comprehensive classification of potential density of integral points based on logarithmic Kodaira dimension and extends the analysis to orbits under endomorphisms assuming the Lang-Vojta conjecture.

Findings

Potential density characterized for im  surfaces.

Integral points lie on finitely many curves when not dense.

Orbit integral points relate to invariant Zariski-closed sets.

Abstract

We analyze when integral points on the complement of a finite union of curves in $\mathbb{P}^2$ are potentially dense. We divide the analysis of these affine surfaces based on their logarithmic Kodaira dimension $\bar{\kappa}$. When $\bar{\kappa} = -\infty$, we completely characterize the potential density of integral points in terms of the number of irreducible components on the surface at infinity and the number of multiple members in a pencil naturally associated to the surface. When integral points are not potentially dense, we show that they lie on finitely many effectively computable curves. When $\bar{\kappa} = 0$, we prove that integral points are always potentially dense. The bulk of our analysis concerns the subtle case of $\bar{\kappa}=1$. We determine the potential density of integral points in a number of cases and develop tools for studying integral points on surfaces fibered over a curve. Finally, nondensity of integral points in the case $\bar{\kappa}=2$ is predicted by the Lang-Vojta conjecture, to which we have nothing new to add. In a related direction, we study integral points in orbits under endomorphisms of $\mathbb{P}^2$. Assuming the Lang--Vojta conjecture, we prove that an orbit under an endomorphism $\phi$ of $\mathbb{P}^2$ can contain a Zariski-dense set of integral points (with respect to some nontrivial effective divisor) only if there is a nontrivial completely invariant proper Zariski-closed set with respect to $\phi$. This may be viewed as a generalization of a result of Silverman on integral points in orbits of rational functions. We provide many specific examples, and end with some open problems.