The anisotropy conjecture for homology spheres

From papers

Let F\mathbb{F} be a field, and let Δ\Delta be an F\mathbb{F}-homology sphere of dimension d1d-1. Write k=F(ai,j)\mathbf{k}=\mathbb{F}(a_{i,j}) for the field of rational functions in variables ai,ja_{i,j}, let k[Δ]\mathbf{k}[\Delta] be the Stanley–Reisner ring of Δ\Delta over k\mathbf{k}, and set

k(Δ)=k[Δ]/(θ1,,θd),\mathbf{k}(\Delta)=\mathbf{k}[\Delta]/(\theta_1,\dots,\theta_d),

where θi=j=1mai,jxj\theta_i=\sum_{j=1}^m a_{i,j}x_j. The sphere Δ\Delta is generically anisotropic over F\mathbb{F} if, for every integer jj with 12jd1\leq 2j\leq d and every nonzero uk(Δ)ju\in\mathbf{k}(\Delta)_j, one has u20u^2\neq 0.

Anisotropy conjecture. For an arbitrary field F\mathbb{F}, any F\mathbb{F}-homology sphere is generically anisotropic over F\mathbb{F}.

This conjecture would extend the theorem of Papadakis and Petrotou, which establishes generic anisotropy for homology spheres over fields of characteristic 22, and would provide the generic-anisotropy route to the strong Lefschetz property and the gg-conjecture in arbitrary characteristic.

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Sources & referencesView supporting material

Primary source

Feifei Fan, “The generic anisotropy of strongly edge decomposable spheres”, arXiv:2406.18989 (2024).

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