Galois-orbit lower bound for Hecke translates

Let (G,X)(\mathbf G,X) be a Shimura datum and let SS be an associated Shimura variety component. Let (H,XH)(G,X)(\mathbf H,X_{\mathbf H})\subset(\mathbf G,X) be a sub-Shimura datum, and for each γG(Q)+\gamma\in\mathbf G(\mathbb Q)_+ let SH,γ=π(γXH+)SS_{\mathbf H,\gamma}=\pi(\gamma X_{\mathbf H}^+)\subset S. Let ρ:GGLn,Q\rho:\mathbf G\to\mathbf{GL}_{n,\mathbb Q} be faithful, and define

N(γ)=max(denomρ(γ),detρ(γ)denomρ(γ)n).N(\gamma)=\max\bigl(\operatorname{denom}\rho(\gamma),\lvert\det\rho(\gamma)\cdot\operatorname{denom}\rho(\gamma)^n\rvert\bigr).

For ΩG(Q)+\Omega\subset\mathbf G(\mathbb Q)_+ and ΣγΩSH,γ\Sigma\subset\bigcup_{\gamma\in\Omega}S_{\mathbf H,\gamma}, define N(s)=min{N(γ):γΩ, sSH,γ}N(s)=\min\{N(\gamma):\gamma\in\Omega,\ s\in S_{\mathbf H,\gamma}\}. Let VSV\subset S be an irreducible algebraic curve not contained in any proper special subvariety, and let LL be a finitely generated characteristic-zero field over which VV is defined. Galois-orbit conjecture. There exist constants C1,C2>0C_1,C_2>0 such that for every sVΣs\in V\cap\Sigma,

#(Aut(C/L)s)C1N(s)C2.\#\bigl(\operatorname{Aut}(\mathbb C/L)\cdot s\bigr)\ge C_1N(s)^{C_2}.

This conjectural lower bound is an arithmetic ingredient in the Pila–Zannier strategy for restricted Zilber–Pink statements; the paper establishes it only in selected settings, so it remains open in the stated generality.

Sources & referencesView supporting material

Primary source

Martin Orr, “Unlikely intersections with Hecke translates of a special subvariety”, arXiv:1710.04092 (2018).

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