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

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

GR‾s(X)=V0s×⋯×Vr−1s\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(Vr−1s),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=Dom⁡i+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.

References

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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