The geometric Breuil–Mézard conjecture for crystalline special fibres

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Let ρ\boldsymbol{\rho} range over residual representations and let λ\boldsymbol{\lambda} range over regular tuples of labeled Hodge–Tate weights. For each Serre weight k\boldsymbol{k}, let ZkZ_{\boldsymbol{k}} be a cycle in Xd,red\mathcal{X}_{d,\mathrm{red}}, and let nkcrys(λ)n_{\boldsymbol{k}}^{\mathrm{crys}}(\boldsymbol{\lambda}) denote the multiplicity of the Serre weight k\boldsymbol{k} in the reduction of the crystalline algebraic representation attached to λ\boldsymbol{\lambda}. The geometric Breuil–Mézard conjecture. There are cycles ZkZ_{\boldsymbol{k}} in Xd,red\mathcal{X}_{d,\mathrm{red}} such that, for every regular tuple of labeled Hodge–Tate weights λ\boldsymbol{\lambda}, the underlying cycle of the special fibre of Xdcrys,λ\mathcal{X}_d^{\mathrm{crys},\boldsymbol{\lambda}} is

∑knkcrys(λ)⋅Zk.\sum_{\boldsymbol{k}}n_{\boldsymbol{k}}^{\mathrm{crys}}(\boldsymbol{\lambda})\cdot Z_{\boldsymbol{k}}.

This is the stack-theoretic geometric refinement of the Breuil–Mézard conjecture: it predicts the cycles, and hence their multiplicities, uniformly across crystalline deformation conditions. The source does not state whether it is resolved.

References

Primary source

Matthew Emerton and Toby Gee, “Moduli stacks of étale (phi,Gamma)-modules and the existence of crystalline lifts”, arXiv:1908.07185 (2022).

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