Groups acting on hyperbolic spaces—a survey

Abstract

This is a (very subjective) survey paper for nonspecialists, covering group actions on Gromov hyperbolic spaces. The first section is about hyperbolic groups themselves, while the rest of the paper focuses on mapping class groups and $\mathrm{Out}(F_n)$, and the way to understand their large scale geometry using their actions on various hyperbolic spaces constructed using projection complexes. This understanding for $\mathrm{Out}(F_n)$ significantly lags behind that of mapping class groups, and the paper ends with a few open questions.