The coarse median structures conjecture for mapping class groups

Let SS be a non-sporadic finite-type surface, and let MCG(S)\operatorname{MCG}(S) denote its mapping class group. A coarse median structure on a group is a coarse median operation compatible with a compatible word metric. Coarse median structures conjecture. The mapping class group MCG(S)\operatorname{MCG}(S) has at least two coarse median structures. This would extend the paper's result for the mapping class group of the five-holed sphere and suggest that non-sporadic mapping class groups support genuinely distinct coarse geometric structures. The statement is presented as a future direction and is not resolved here.

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Primary source

Giorgio Mangioni, “Short hierarchically hyperbolic groups I: uncountably many coarse median structures”, arXiv:2410.09232 (2025).

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