Breuil–Mézard conjecture for two-dimensional Galois representations

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 ρL:GLGL2(F)\overline{\rho}_L:G_L\to\mathrm{GL}_2(\mathbb{F}) be a continuous representation. For a weight λ(Z+2)HomQp(L,E)\lambda\in(\mathbb{Z}_+^2)^{\operatorname{Hom}_{\mathbb{Q}_p}(L,E)} and an inertia type τ\tau, let RρLcrys,λ,τR^{\mathrm{crys},\lambda,\tau}_{\overline{\rho}_L} and RρLss,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(ρL)\mu_k(\overline{\rho}_L) be the Breuil–Mézard multiplicities. Breuil–Mézard conjecture. For every such λ\lambda and τ\tau,

e(RρLcrys,λ,τ/ϖ)=kWLnkcrys(λ,τ)μk(ρL),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(RρLss,λ,τ/ϖ)=kWLnkss(λ,τ)μk(ρL).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.

Sources & referencesView supporting material

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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