Nontriviality conjecture for the associahedral class in the curve complex

Let Σg1\Sigma_g^1 be a genus-gg surface with one boundary component, and let C(Σg1)\mathcal{C}(\Sigma_g^1) denote its curve complex. For the simplicial map qq from the boundary Θ\Theta of the dual of the (2g1)(2g-1)-dimensional associahedron to C(Σg1)\mathcal{C}(\Sigma_g^1) described in the source, write [q][q] for its homotopy class in reduced homology.

Nontriviality conjecture. For g1g \geq 1, the class

[q]H~2g2(C(Σg1);Z)[q] \in \widetilde{\mathrm{H}}_{2g-2}(\mathcal{C}(\Sigma_g^1);\mathbb{Z})

is nontrivial. When g=1g=1, the corresponding picture consists of 22 pairs of parallel curves.

This proposes an explicit homologically nontrivial sphere in the curve complex, avoiding the increasingly impractical direct construction from the earlier proposition. The source gives no resolution of the claim.

Sources & referencesView supporting material

Primary source

Nathan Broaddus, “Homology of the curve complex and the Steinberg module of the mapping class group”, arXiv:0711.0011 (2011).

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