Discriminant-negligibility of heights of special points on Shimura varieties

Let (G,X)(\mathbf{G},\mathbf{X}) be a Shimura datum with G\mathbf{G} semisimple of adjoint type, let KK be a compact open subgroup of G(Af)\mathbf{G}(\mathbb A_f), let XX be a connected component of X\mathbf{X}, and set S=Γ\XS=\Gamma\backslash X, where Γ=KG(Q)+\Gamma=K\cap\mathbf{G}(\mathbb Q)^+. Let pSp\in S be a special point, write p=π(x)p=\pi(x) with xx in a fixed semialgebraic fundamental set, and let T\mathbf{T} be the Mumford–Tate torus of xx. If KTmK^m_{\mathbf{T}} is the maximal compact open subgroup of T(Af)\mathbf{T}(\mathbb A_f), KT=KT(Af)K_{\mathbf{T}}=K\cap\mathbf{T}(\mathbb A_f), LL is the splitting field of T\mathbf{T}, and dLd_L is the absolute value of its discriminant, define

disc(p)=[KTm:KT]dL.\operatorname{disc}(p)=[K^m_{\mathbf{T}}:K_{\mathbf{T}}]d_L.

Discriminant-negligibility conjecture. There exists a Weil height function h ⁣:S(Q)Rh\colon S(\overline{\mathbb Q})\to\mathbb R such that, for every special point pSp\in S and every ε>0\varepsilon>0,

h(p)=OS,ε(disc(p)ε).h(p)=O_{S,\varepsilon}(\operatorname{disc}(p)^\varepsilon).

Thus the heights of special points grow sub-polynomially in their discriminants. Assuming this conjecture, the paper derives lower bounds for Galois orbits of special points and a new point-counting proof of the André–Oort conjecture for Shimura varieties of abelian type; the conjecture itself remains open in the supplied text.

Sources & referencesView supporting material

Primary source

Gal Binyamini, Harry Schmidt and Andrei Yafaev, “Lower bounds for Galois orbits of special points on Shimura varieties: a point-counting approach”, arXiv:2104.05842 (2021).

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