Exponential-polynomial equations and dynamical return sets

Abstract

We show that for each finite sequence of algebraic integers ${\alpha }_1,...,{\alpha }_n$ and polynomials $P_1(x_1,...,x_n;y_1,...,y_n),...,P_r(x_1,...,x_n;y_1,...,y_n)$ with algebraic integer coefficients, there are a natural number $N$, $n$ commuting endomorphisms $Φ_i:\Gm^N \to \Gm^N$ of the $N^{\text{th}}$ Cartesian power of the multiplicative group, a point $P \in \Gm^N(\QQ)$, and an algebraic subgroup $G \leq \Gm^N$ so that the return set $\{(\ell_1,...,\ell_n) \in \NN^n : Φ_1^{\circ \ell_1} \circ... \circ Φ_n^{\circ \ell_n}(P) \in G(\QQ) \}$ is identical to the set of solutions to the given exponential-polynomial equation: $\{(\ell_1,...,\ell_n) \in \NN^n : P_1(\ell_1,...,\ell_n;α_1^{\ell_1},...,α_n^{\ell_n}) = ... = P_r(\ell_1,...,\ell_n;α_1^{\ell_1},...,α_n^{\ell_n}) = 0 \}$.