Actions of right-angled Artin groups in low dimensions

We survey the role of right-angled Artin groups in the theory of diffeomorphism groups of low dimensional manifolds. We first describe some of the subgroup structure of right-angled Artin groups. We then discuss the interplay between algebraic structure, compactness, and regularity for group actions on one–dimensional manifolds. For compact one–manifolds, every right-angled Artin group acts faithfully by C1 diffeomorphisms, but the right-angled Artin groups which act faithfully by C2 diffeomorphisms are very restricted. For the real line, every right-angled Artin group acts faithfully by C8 diffeomorphisms, though analytic actions are again more limited. In dimensions two and higher, every right-angled Artin group acts faithfully on every manifold by C8 diffeomorphisms. We give applications of this discussion to mapping class groups of surfaces and related groups.