Iteration and the Minimal Resultant

Let $K$ be an algebraically closed field that is complete with respect to a non-Archimedean absolute value, and let $\phi \in K(z)$ have degree $d\geq 2$\mathrm{.}Wecharacterizemapsforwhichtheminimalresultantofaniterate$\varphi^n$isgivenbyasimpleformulaintermsof$d$,$n$, and the minimal resultant of $\phi$. We show that such maps are precisely those with reduction outside of an indeterminacy locus $I(d)$ and which also have semi-stable reduction for every iterate ${\phi }^n$. We give two equivalent ways of describing such maps, one measure theoretic and the other in terms of the moduli space ${\mathcal{M}}_d$ of degree $d$ rational maps. As an application, we are able to give an explicit formula for the minimal value of the diagonal Arakelov-Green’s function of a map satisfying the conditions of the main theorem. We illustrate our results with some explicit calculations in the case of the Latt`es maps.