Definable functions in tame expansions of algebraically closed valued fields

Abstract

In this article we study definable functions in tame expansions of algebraically closed valued fields. For a given definable function we have two types of results: type (I), which hold in a neighborhood of infinity, and type (II), which hold locally for all but finitely many points in the domain of the function. In the first part of the article, we show type (I) and (II) results concerning factorizations of definable functions over the value group. As an application, we show that tame expansions of algebraically closed valued fields having value group ℚ (like ℂ_p and $\overline{\mathbb{F}_p}^{\rm{alg}}((t\mathbb{C}))$) are polynomially bounded. In the second part, under an additional assumption on the asymptotic behavior of unary definable functions of the value group, we lift these factorizations over the residue multiplicative structure RV. In characteristic 0, we obtain as a corollary that the domain of a definable function f: X ⊆ K → K can be partitioned into sets F ∪ E ∪ J, where F is finite, fE is locally constant and fJ satisfies locally the Jacobian property.