The tensor-product conjecture for deformation rings of stratified Kisin varieties

Let X\mathbb{X} be a fixed nondegenerate gene, and write its stratified embedded Kisin variety as

GRs(X)=V0s××Vr1s\overline{\mathcal{G}\mathcal{R}}^{\mathrm{s}}(\mathbb{X})=\mathcal V^{\mathrm{s}}_0\times\cdots\times\mathcal V^{\mathrm{s}}_{r-1}

inside (P1)f(\mathbb{P}^1)^f. Let Rψ(t,ρ)R^{\psi}({\rm t},\overline\rho) and Dψ(t,ρ)D^{\psi}({\rm t},\overline\rho) denote the potentially Barsotti–Tate deformation ring and its generic fibre. Tensor-product conjecture. The following hold:

Rψ(t,ρ)R(V0s)^OE^OER(Vr1s),R^{\psi}({\rm t},\overline\rho)\simeq R(\mathcal V^{\mathrm{s}}_0)\mathbin{\widehat\otimes}_{\mathcal O_E}\cdots\mathbin{\widehat\otimes}_{\mathcal O_E}R(\mathcal V^{\mathrm{s}}_{r-1}),

where each R(Vjs)R(\mathcal V^{\mathrm{s}}_j) is a local noetherian complete OE\mathcal O_E-algebra depending only on Vjs\mathcal V^{\mathrm{s}}_j. 2. Rψ(t,ρ)R^{\psi}({\rm t},\overline\rho) is the ring of power-bounded functions on Dψ(t,ρ)D^{\psi}({\rm t},\overline\rho) if there is no index ii with Xi=Xi+f=Domi+1(X)X_i=X_{i+f}=\operatorname{Dom}_{i+1}(\mathbb{X}).

The conjecture is a weaker integral refinement of the proposed product decomposition of the generic fibre. The source gives no resolution.

Sources & referencesView supporting material

Primary source

Xavier Caruso, Agnès David and Ariane Mézard, “Combinatorics of Serre weights in the potentially Barsotti-Tate setting”, arXiv:2105.04147 (2021).

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