Mixed hybrid conjecture for universal abelian schemes

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Let AA be an abelian variety over C{\mathbb C}, and let P∈A(C)P\in A({\mathbb C}). Let HΓ(A,P)H_{\Gamma}(A,P) be as in the definition referenced in the source, and let Σ⊆HΓ(A,P)\Sigma\subseteq H_{\Gamma}(A,P) be a subset. Let V⊆Σ‾Zar⁡V\subseteq \overline{\Sigma}^{\operatorname{Zar}} be an irreducible component, and let S⊆AΓS\subseteq {\mathbb A}_\Gamma be the image of VV.

Mixed hybrid conjecture. (1) The subvariety S⊆AΓS\subseteq {\mathbb A}_\Gamma is weakly special. (2) If, for some s∈Ss\in S, one has V∩(As)tors⁡≠∅V\cap (A_s)_{\operatorname{tors}}\neq\varnothing, then there exist d∈Z≥1d\in {\mathbb Z}_{\geq 1} and an abelian subscheme B≤AΓ∣S\mathcal{B}\leq \mathcal{A}_\Gamma|_S such that

d⋅V=B.d\cdot V=\mathcal{B}.

Equivalently, VV is an irreducible component of

B+AΓ∣S[d].\mathcal{B}+\mathcal{A}_\Gamma|_S[d].

(3) In general, if η∈S\eta\in S is the generic point of SS and Vη⊆AηV_\eta\subseteq \mathcal{A}_\eta is the fibre of V⊆AΓV\subseteq \mathcal{A}_\Gamma over η\eta, then there exist d∈Z≥1d\in {\mathbb Z}_{\geq 1}, a morphism ϕ:A→Aη\phi:A\to \mathcal{A}_\eta, and an abelian subvariety B≤AηB\leq A_\eta such that

d⋅Vη=ϕ(P)+B⊆Aη.d\cdot V_\eta=\phi(P)+B\subseteq \mathcal{A}_\eta.

The first part is established by the cited theorem on the hybrid conjecture for AΓ{\mathbb A}_\Gamma; the torsion and general fibre assertions describe the remaining mixed hybrid conjecture. The supplied context does not establish their resolution.

References

Primary source

Rodolphe Richard and Andrei Yafaev, “Hybrid Conjecture in a Mixed Shimura variety”, arXiv:2604.23376 (2026).

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