University of Arkansas Topology Seminar: 3/12/2020

Speaker: Corey Bregman

Title: An outer space for right-angled Artin groups

The classical symmetric space Qn of positive definite inner products on ℝn admits a properly discontinuous action of GL(n,ℤ), and the topology of the quotient can be used to study properties of this group. A more geometric description of Qn is the space of flat n-tori together with a basis for the fundamental group. By analogy with Qn, Culler-Vogtmann outer space CVn parametrizes rank n, metric graphs together with a choice of free basis for their fundamental group. CVn has been an indispensable tool for understanding the outer automorphism groups of free groups. Right-angled Artin groups (raags) are a well-studied family of groups containing both free groups and free abelian groups, which have recently featured prominently in low-dimensional topology. For each raag A we construct a finite-dimensional outer space, parametrizing certain CAT(0) cube complexes equipped with a cocompact action of A. This is joint work with Ruth Charney and Karen Vogtmann.



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