The CM-lift conjecture for Hodge classes on abelian varieties

Let ww be a prime of Qal\mathbb{Q}^{\mathrm{al}} and let AA be an abelian variety over Qal\mathbb{Q}^{\mathrm{al}} with good reduction at ww. Let γ\gamma be a Hodge class on AA. Two pairs (A,γ)(A,\gamma) and (A,γ)(A',\gamma') have isogenous specializations preserving the classes if there is an isogeny A0A0A_{0}\to A'_{0} sending γ0\gamma_{0} to γ0\gamma'_{0}. The CM-lift conjecture. There exist a CM abelian variety AA' over Qal\mathbb{Q}^{\mathrm{al}} and a Hodge class γ\gamma' on AA' such that (A,γ)0(A,\gamma)_{0} and (A,γ)0(A',\gamma')_{0} have isogenous specializations preserving the classes. This refines the fact that abelian varieties over the residue field lift up to isogeny to CM abelian varieties; the source gives approaches and partial cases but does not state a general proof.

Sources & referencesView supporting material

Primary source

James S. Milne, “Abelian motives and Shimura varieties in nonzero characteristic”, arXiv:2508.09972 (2025).

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