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

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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 ⁣:A→A∨\lambda\colon A\to A^\vee be a principal polarization. For each a∈A2a\in A_2, let id⁡κ(a)\operatorname{id}_{\kappa(a)} denote the base change of id⁡ ⁣:A→A\operatorname{id}\colon A\to A to κ(a)\kappa(a). Arithmetic signed count conjecture. One has

∑a∈A2Tr⁡κ(a)/k(deg⁡aA1(id⁡κ(a),λ(a)))=2g−1⋅((2g+1)⋅⟨1⟩+(2g−1)⋅⟨−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.

References

Primary source

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

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