Breuil–Mézard conjecture for two-dimensional Galois representations

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Let L/QpL/\mathbb{Q}_p be a finite extension, let EE be a coefficient field, let WLW_L be the set of Serre weights, and let ρ‾L:GL→GL2(F)\overline{\rho}_L:G_L\to\mathrm{GL}_2(\mathbb{F}) be a continuous representation. For a weight λ∈(Z+2)Hom⁡Qp(L,E)\lambda\in(\mathbb{Z}_+^2)^{\operatorname{Hom}_{\mathbb{Q}_p}(L,E)} and an inertia type τ\tau, let Rρ‾Lcrys,λ,τR^{\mathrm{crys},\lambda,\tau}_{\overline{\rho}_L} and Rρ‾Lss,λ,τR^{\mathrm{ss},\lambda,\tau}_{\overline{\rho}_L} be the corresponding crystalline and semistable deformation rings, let nkcrys(λ,τ)n_k^{\mathrm{crys}}(\lambda,\tau) and nkss(λ,τ)n_k^{\mathrm{ss}}(\lambda,\tau) be the specified multiplicities, and let μk(ρ‾L)\mu_k(\overline{\rho}_L) be the Breuil–Mézard multiplicities. Breuil–Mézard conjecture. For every such λ\lambda and τ\tau,

e(Rρ‾Lcrys,λ,τ/ϖ)=∑k∈WLnkcrys(λ,τ)μk(ρ‾L),e(R^{\mathrm{crys},\lambda,\tau}_{\overline{\rho}_L}/\varpi)=\sum_{k\in W_L}n_k^{\mathrm{crys}}(\lambda,\tau)\mu_k(\overline{\rho}_L),

and

e(Rρ‾Lss,λ,τ/ϖ)=∑k∈WLnkss(λ,τ)μk(ρ‾L).e(R^{\mathrm{ss},\lambda,\tau}_{\overline{\rho}_L}/\varpi)=\sum_{k\in W_L}n_k^{\mathrm{ss}}(\lambda,\tau)\mu_k(\overline{\rho}_L).

The conjecture predicts Hilbert–Samuel multiplicities of deformation rings from Serre-weight multiplicities. The supplied text recalls results identifying the crystalline weight support and cites established theorems for parts of the framework, but does not resolve the displayed general formulas.

References

Primary source

Kojiro Matsumoto, “On the classicality theorem and its applications to the automorphy lifting theorem and the Breuil-Mezard conjecture in some GL_2(Q_p^2) cases”, arXiv:2512.04641 (2025).

Additional references

4 papers in this index state this conjecture (2011–2025). The statement above is taken from the most recent of them; the others are arXiv:1309.1658, arXiv:1309.0019, arXiv:1109.4226.

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