The local model conjecture for parahoric local Shimura pairs

Let (G,{μ})(G,\{\mu\}) be a local Shimura pair, let KK be a parahoric subgroup of G(Qp)G(\mathbb Q_p), and let G{\mathcal G} be the corresponding parahoric group scheme over Spec(Zp)\operatorname{Spec}(\mathbb Z_p), with K=G(Zp)K={\mathcal G}(\mathbb Z_p). Write EE for the local reflex field, OE{\mathcal O}_E for its ring of integers, and kk for the residue field. Let AdmK~({μ}){\rm Adm}_{\tilde K}(\{\mu\}) denote the associated admissible set, and let XμX_\mu be the generic-fiber Schubert variety.

The local model conjecture. There exists a projective and flat scheme

MK(G,{μ}){\rm M}_K(G,\{\mu\})

over

Spec(OE){\rm Spec}({\mathcal O}_E)

which supports an action of GZpOE{\mathcal G}\otimes_{\mathbb Z_p}{\mathcal O}_E and is such that: (i) the generic fiber MK(G,{μ})OEE{\rm M}_K(G,\{\mu\})\otimes_{{\mathcal O}_E}E is GEG_E-isomorphic to XμX_\mu; (ii) there is a K~\tilde K-equivariant bijection between MK(G,{μ})(k){\rm M}_K(G,\{\mu\})(k) and

{gK~G(L)/K~K~gK~AdmK~({μ})}G(L)/K~.\{g\tilde K\in G(L)/\tilde K\mid \tilde K g\tilde K\in {\rm Adm}_{\tilde K}(\{\mu\})\}\subset G(L)/\tilde K.

This is a foundational conjecture relating integral local models to affine Grassmannian Schubert strata. The source presents it as an expected construction; no resolution is supplied in the given text.

Sources & referencesView supporting material

Primary source

Georgios Pappas, “Arithmetic models for Shimura varieties”, arXiv:1804.04717 (2018).

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