Mathematics – Dynamical Systems
Scientific paper
2009-01-15
Mathematics
Dynamical Systems
Some references have been added and others updated. Numerous typos, grammatical errors, and minor misstatements have been corr
Scientific paper
We study algebraic dynamical systems (and, more generally, $\sigma$-varieties) $\Phi:{\mathbb A}^n_{\mathbb C} \to {\mathbb A}^n_{\mathbb C}$ given by coordinatewise univariate polynomials, $\Phi(x_1,...,x_n) = (f_1(x_1),...,f_n(x_n))$ by refining an old theorem of Ritt on compositional identities amongst polynomials. Our main result is an explicit description of the skew-invariant varieties, that is, for a field automorphism $\sigma:{\mathbb C} \to {\mathbb C}$ we describe those algebraic varieties $X \subseteq {\mathbb A}^n_{\mathbb C}$ such that $\Phi(X) = X^\sigma$. In particular, taking $\sigma$ to be the identity function, we characterize the $\Phi$-invariant varieties. As consequences, we deduce a variant of a conjecture of Zhang on the existence of rational points with Zariski dense forward orbits, a strong form of the dynamical Manin-Mumford conjecture for liftings of the Frobenius, and an answer to the question of definability of nonorthogonality for minimal types in difference closed fields of characteristic zero extending the formula $\sigma(x) = f(x)$ for $f$ a polynomial.
Medvedev Alice
Scanlon Thomas
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