The torsion conjecture for discrete CAT(0)-space isometry groups

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Let XX be a proper, CAT⁡(0)\operatorname{CAT}(0)-space and let Γ\Gamma be a discrete group of isometries of XX, not necessarily cocompact. A group is torsion if it contains only finite-order elements.

Torsion conjecture. If Γ\Gamma is torsion, then Γ\Gamma is finite. An easier version is that if Γ\Gamma is almost-cocompact, then it contains an infinite-order element.

The conjecture concerns whether properness and discreteness impose finiteness on torsion isometry groups; the paper presents the almost-cocompact assertion as the version needed for its application. No resolution is given in the supplied context.

References

Primary source

Nicola Cavallucci and Andrea Sambusetti, “Thin actions on CAT(0) spaces”, arXiv:2210.01085 (2022).

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