Strictness conjectures for hyperbolic structures on spherical Artin–Tits groups

Let A=ASA=A_S be an irreducible Artin–Tits group of spherical type with rank at least 33. Let XabsAX_{abs}^A be the absorbable-element generating set, XNPAX_{NP}^A the union of normalizers of proper irreducible standard parabolic subgroups, and XPAX_P^A the union of proper irreducible standard parabolic subgroups together with the cyclic subgroup generated by ΔS2\Delta_S^2. Write XYX\preccurlyeq Y when the identity map from (A,dY)(A,d_Y) to (A,dX)(A,d_X) is Lipschitz. Strictness conjectures. (i) The inequality XabsAXNPAX_{abs}^A\preccurlyeq X_{NP}^A is not strict: XNPAXabsAX_{NP}^A\preccurlyeq X_{abs}^A also holds, and the identity map Γ(A,XNPA)Γ(A,XabsA)\Gamma(A,X_{NP}^A)\to\Gamma(A,X_{abs}^A) is a quasi-isometry. (ii) The inequality XNPAXPAX_{NP}^A\preccurlyeq X_P^A is strict: the identity map Γ(A,XPA)Γ(A,XNPA)\Gamma(A,X_P^A)\to\Gamma(A,X_{NP}^A) is Lipschitz but not a quasi-isometry. These claims compare the large-scale geometry of three hyperbolic structures; the source presents them as open problems, with the braid-group instance in (i) relating the additional length graph to the curve graph of the punctured disk.

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Primary source

Matthieu Calvez and Bert Wiest, “Hyperbolic structures for Artin-Tits groups of spherical type”, arXiv:1904.02234 (2019).

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