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Boundary Dynamics, Cubical Actions, and Infinite Girth

Tattwamasi Amrutam, Arka Banerjee, Daniel L. Gulbrandsen, Pratyush Mishra

math.GRarXiv:2608.31124

Abstract

We develop two methods for proving infinite girth from boundary dynamics. First, we use topologically free extreme boundary actions to give a boundary-dynamical proof of infinite girth for finitely generated acylindrically hyperbolic groups. The second combines Nakamura's criterion with, respectively, flag-space and Roller-boundary dynamics, yielding infinite-girth results for semisimple S-algebraic groups and for essential non-elementary actions on finite-dimensional, second countable, non-Euclidean CAT(0) cube complexes. We also prove that every finitely generated large group has infinite girth, thereby answering a question of Akhmedov and Mishra.

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