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

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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:

lim⁡q→∞q oddΠ3(q)=lim⁡q→∞q 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}, lim⁡q→∞q evenΠ3(q)=lim⁡q→∞q 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.

References

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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