The wild McKay point-counting conjecture for quotient singularities

Let KK be a local field with finite residue field κ\kappa of cardinality qq, let τ:ΓGLnOK\tau:\Gamma\to\operatorname{GL}_n\mathcal{O}_K be a faithful representation of a finite group Γ\Gamma, and let X:=AOKn/ΓX:=\mathbb{A}_{\mathcal{O}_K}^n/\Gamma. Suppose that for every gΓ{1}g\in\Gamma\setminus\{1\}, the fixed-point locus (AOKn)g(\mathbb{A}_{\mathcal{O}_K}^n)^g has codimension at least two, and let f:YXf:Y\to X be a crepant resolution. Write ZYZ\subset Y for the preimage of the origin 0X(κ)0\in X(\kappa). For a continuous homomorphism ρ:GKΓ\rho:G_K\to\Gamma, let wτ(ρ)\mathbf{w}_\tau(\rho) denote its weight, and let M(K,Γ,wτ)M(K,\Gamma,-\mathbf{w}_\tau) be the corresponding mass.

Point-counting realization of the wild McKay conjecture. If the residue field κ\kappa is finite, then

Z(κ)=M(K,Γ,wτ).\sharp Z(\kappa)=M(K,\Gamma,-\mathbf{w}_\tau).

This is the finite-residue-field point-counting form of the motivic wild McKay correspondence, relating the special fiber of a crepant resolution to a weighted count of Γ\Gamma-torsors over SpecK\operatorname{Spec}K. It is posed as a consequence of the motivic conjecture and remains unresolved in the stated generality.

Sources & referencesView supporting material

Primary source

Melanie Machett Wood and Takehiko Yasuda, “Mass formulas for local Galois representations and quotient singularities I: a comparison of counting functions”, arXiv:1309.2879 (2015).

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