BGGH's conjecture on Cannon–Thurston maps for HHG pairs

Let GG be a hierarchically hyperbolic group (HHG), and let H<GH<G be an infinite hyperbolic normal subgroup of infinite index. A Cannon–Thurston map is a continuous extension of the inclusion HGH\hookrightarrow G to the relevant hierarchical boundaries. BGGH's conjecture. The Cannon–Thurston map does not exist for (H,G)(H,G) unless either GG is hyperbolic or HH is hierarchically quasiconvex in some HHG structure on GG. This conjecture concerns the existence of boundary extensions for hyperbolic normal subgroups of infinite index in HHGs; the supplied source does not state whether it has been resolved.

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Primary source

Funda Gültepe and Ravi Tomar, “Non-existence of Cannon-Thurston maps for hierarchically hyperbolic groups”, arXiv:2607.22447 (2026).

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