Arithmetic signed count conjecture for 2-torsion points on principally polarized abelian varieties

Let AA be an abelian variety of dimension gg over a field kk with char(k)2\operatorname{char}(k)\neq 2, and let λ ⁣:AA\lambda\colon A\to A^\vee be a principal polarization. For each aA2a\in A_2, let idκ(a)\operatorname{id}_{\kappa(a)} denote the base change of id ⁣:AA\operatorname{id}\colon A\to A to κ(a)\kappa(a). Arithmetic signed count conjecture. One has

aA2Trκ(a)/k(degaA1(idκ(a),λ(a)))=2g1((2g+1)1+(2g1)1).\sum_{a\in A_2}\operatorname{Tr}_{\kappa(a)/k}\bigl(\deg_{a}^{{\mathbb A}^1}(\operatorname{id}_{\kappa(a)},\lambda(a))\bigr)=2^{g-1}\cdot\bigl((2^g+1)\cdot\langle1\rangle+(2^g-1)\cdot\langle-1\rangle\bigr).

This conjecture proposes an arithmetic refinement of the signed count of the 2-torsion points of a principally polarized abelian variety, with the local degrees valued in the Grothendieck–Witt group. The supplied text gives no resolution status or further evidence, so its status remains open.

Sources & referencesView supporting material

Primary source

Mario Kummer, “A signed count of 2-torsion points on real abelian varieties”, arXiv:2301.10621 (2023).

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