Milne's rationality conjecture for absolute Hodge classes

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Let AA be an abelian variety over Qal\mathbb{Q}^{\mathrm{al}} with good reduction A0A_0 over Fal\mathbb{F}^{\mathrm{al}}, let d=dim⁡(A)d=\dim(A), and let γ\gamma be an absolute Hodge class of codimension ii on AA. Let γl∈H2i(A0,Ql(i))\gamma_l\in H^{2i}(A_0,\mathbb{Q}_l(i)) for l≠pl\ne p and γp∈Hcrys2i(A0/W)(i)Q\gamma_p\in H_{\mathrm{crys}}^{2i}(A_0/W)(i)_{\mathbb{Q}} be its specializations. For divisors D1,…,Dd−iD_1,\ldots,D_{d-i} on A0A_0, write δm(l)\delta_m(l) for their ll-cohomology classes. Rationality conjecture. The intersection number

γl⋅δ1(l)⋯δd−i(l)\gamma_l\cdot\delta_1(l)\cdots\delta_{d-i}(l)

which a priori lies in Ql\mathbb{Q}_l or (Qal)w(\mathbb{Q}^{\mathrm{al}})_w, is a rational number independent of ll. This conjecture concerns compatibility of realizations of absolute Hodge classes under reduction and is used in constructing motivic categories with rational Tate classes. Its general status is not resolved in the supplied text.

References

Primary source

James Milne and Niranjan Ramachandran, “Motivic complexes and special values of zeta functions”, arXiv:1311.3166 (2013).

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The manuscript claims Milne's rationality conjecture for abelian varieties over the algebraic numbers with good reduction in every residue characteristic, including two. For each fixed reduction and rational Hodge class, its pairing with every complementary divisor product is the same rational number in all prime-to-p realizations and crystalline cohomology.

GitHub repository: https://github.com/openai/math

Manuscript: https://github.com/openai/math/blob/adc7f1241b42e322a6451854ab7e4b4c146bf78a/preprints/Milnes-rationality-conjecture-for-abelian-varieties-September-23-2026/paper.pdf

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