Asymptotic proportions of non-hyperelliptic isogeny classes and obstruction-rule polynomials

From papers

Let Π3(q)\Pi_3(q) be the proportion of isogeny classes of 33-dimensional abelian varieties over Fq\mathbb{F}_q that do not contain the Jacobian of a genus-33 hyperelliptic curve. Let χ3(q)\chi_3(q) be the proportion of degree-66 qq-Weil polynomials for which rule 1.N.N.0\textbf{1.N.N.0} holds when qq is odd and rule 0.N.N.0\textbf{0.N.N.0} holds when qq is even. Asymptotic proportion conjecture. The following limits hold:

limqq oddΠ3(q)=limqq oddχ3(q)=14,\lim_{\substack{q\to\infty \\ q\ \mathrm{odd}}}\Pi_3(q)=\lim_{\substack{q\to\infty \\ q\ \mathrm{odd}}}\chi_3(q)=\frac{1}{4}, limqq evenΠ3(q)=limqq evenχ3(q)=12.\lim_{\substack{q\to\infty \\ q\ \mathrm{even}}}\Pi_3(q)=\lim_{\substack{q\to\infty \\ q\ \mathrm{even}}}\chi_3(q)=\frac{1}{2}.

These limits quantify the expected asymptotic proportion of non-hyperelliptic isogeny classes and of Weil polynomials detected by the relevant rule; the conjecture is part of the paper's statistical analysis and remains open.

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Sources & referencesView supporting material

Primary source

Matvey Borodin and Liam May, “Hyperelliptic Jacobians in Isogeny Classes of Abelian Threefolds Over Finite Fields”, arXiv:2508.16885 (2025).

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