Negative curvature in automorphism groups of one-ended hyperbolic groups

Abstract

In this article, we show that some negative curvature may survive when taking the automorphism group of a finitely generated group. More precisely, we prove that the automorphism group $\mathrm{Aut}(G)$ of a one-ended hyperbolic group $G$ turns out to be acylindrically hyperbolic. As a consequence, given a group $H$ and a morphism $\varphi : H \to \mathrm{Aut}(G)$, we deduce that the semidirect product $G \rtimes_\varphi H$ is acylindrically hyperbolic if and only if $\mathrm{ker}(H \overset{\varphi}{\to} \mathrm{Aut}(G) \to \mathrm{Out}(G))$ is finite.