The Dehn-filling conjecture for mapping class groups

Let SS be any surface of finite type, and let g1,,glMCG(S)g_1,\dots,g_l\in MCG(S). For a subset AA of a group, write A\langle\langle A\rangle\rangle for its normal closure. Dehn-filling conjecture. There exists NN{0}N\in\mathbb{N}-\{0\} such that

MCG(S)/{giN}MCG(S)/\langle\langle \{g_i^{N}\}\rangle\rangle

is hierarchically hyperbolic. This conjecture seeks a general theory of Dehn-filling-like quotients of hierarchically hyperbolic groups, extending known constructions for mapping class groups and potentially producing hyperbolic quotients and applications to algebraic properties such as residual finiteness and the congruence subgroup property.

Sources & referencesView supporting material

Primary source

Alessandro Sisto, “New tools in hierarchical hyperbolicity: A survey”, arXiv:2507.17546 (2025).

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