Locally acyclic cluster algebras

This paper studies cluster algebras locally, by identifying a special class of localizations which are themselves cluster algebras. A `locally acyclic cluster algebra' is a cluster algebra which admits a finite cover (in a geometric sense) by acyclic cluster algebras. Many important results about acyclic cluster algebras extend to local acyclic cluster algebras (such as finite generation, integrally closure, and equaling their upper cluster algebra), as well as results which are new even for acyclic cluster algebras (such as regularity when the exchange matrix has full rank). We develop several techniques for determining whether a cluster algebra is locally acyclic. We show that cluster algebras of marked surfaces with at least two boundary marked points are locally acyclic, providing a large class of examples of cluster algebras which are locally acyclic but not acyclic. We also work out several specific examples in detail.