geometry-topology / Geometric group theory; CAT(0) and CAT(-1) groups

Is every word-hyperbolic group CAT(0)?

Theorem 1.1: there is a finite connected two-dimensional aspherical simplicial complex KK with linear combinatorial disk filling, so π1K\pi_1K is word-hyperbolic with a finite classifying space, such that π1K\pi_1K has no geometric action on any proper complete CAT(0) space in any dimension. Hence it is neither CAT(0) nor CAT(-1), and no finite complex homotopy equivalent to KK carries a locally CAT(0) metric inducing its topology. The group comes from a random-presentation construction with a Fano-plane incidence core and a harmonic-energy fixed-point obstruction. Not shown: an explicit presentation, or which natural classes of hyperbolic groups (for example random or small-cancellation groups) are CAT(0).

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geometry-topologySep 25, 2026Significance 45/100Registry: lean checked

Is every word-hyperbolic group CAT(0)?

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Theorem 1.1: there is a finite connected two-dimensional aspherical simplicial complex KK with linear combinatorial disk filling, so π1K\pi_1K is word-hyperbolic with a finite classifying space, such that π1K\pi_1K has no geometric action on any proper complete CAT(0) space in any dimension. Hence it is neither CAT(0) nor CAT(-1), and no finite complex homotopy equivalent to KK carries a locally CAT(0) metric induci…

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Theorem 1.1: there is a finite connected two-dimensional aspherical simplicial complex KK with linear combinatorial disk filling, so π1K\pi_1K is word-hyperbolic with a finite classifying space, such that π1K\pi_1K has no geometric action on any proper complete CAT(0) space in any dimension. Hence it is neither CAT(0) nor CAT(-1), and no finite complex homotopy equivalent to KK carries a locally CAT(0) metric inducing its topology. The group comes from a random-presentation construction with a Fano-plane incidence core and a harmonic-energy fixed-point obstruction. Not shown: an explicit presentation, or which natural classes of hyperbolic groups (for example random or small-cancellation groups) are CAT(0).

Theorem 1.1: there is a finite connected two-dimensional aspherical simplicial complex KK with linear combinatorial disk filling, so π1K\pi_1K is word-hyperbolic with a finite classifying space, such that π1K\pi_1K has no geometric action on any proper complete CAT(0) space in any dimension. Hence it is neither CAT(0) nor CAT(-1), and no finite complex homotopy equivalent to KK carries a locally CAT(0) metric inducing its topology. The group comes from a random-presentation construction with a Fano-plane incidence core and a harmonic-energy fixed-point obstruction. Not shown: an explicit presentation, or which natural classes of hyperbolic groups (for example random or small-cancellation groups) are CAT(0).

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