A Breuil–Mézard conjecture for discrete series extended types

Let KK be the local field and let GKG_K be its absolute Galois group. Let F\mathbb{F} be the coefficient field, let Γ\Gamma be the relevant Grothendieck group, and let ρ\overline{\rho} be a continuous two-dimensional representation of GKG_K over F\mathbb{F}. For a discrete series inertial type t\texttt{t}, Hodge–Tate type ww, character ψ\psi lifting ω1detρ\omega^{-1}\det\overline{\rho} and compatible with t\texttt{t} and ww, and extended type t+\texttt{t}^+ compatible with (t,ψ)(\texttt{t},\psi), write R,ψ(w,t+,ρ)R^{\square,\psi}(w,\texttt{t}^+,\overline{\rho}) for the corresponding potentially semi-stable deformation ring, and let σG(t)\sigma_{\mathcal{G}}(\texttt{t}) and σw\sigma_w be the associated representations. Breuil–Mézard conjecture for extended types. There exists a positive linear form μρ\mu_{\overline{\rho}} on R(Γ)\mathcal{R}(\Gamma) with values in Z\mathbb{Z} such that, for every such tuple, one can choose σG(t)\sigma_{\mathcal{G}}(\texttt{t}) with

e(R,ψ(w,t+,ρ)/π)=μρ([σG(t)σw]).e(R^{\square,\psi}(w,\texttt{t}^+,\overline{\rho})/\pi)=\mu_{\overline{\rho}}([\overline{\sigma_{\mathcal{G}}}(\texttt{t})\otimes\overline{\sigma_w}]).

If ρ\overline{\rho} is not a twist of an extension of the trivial character by the cyclotomic character, then the multiplicities for conjugate extended types agree:

e(R,ψ(w,t+,ρ)/π)=e(R,ψ(w,t,ρ)/π),e(R^{\square,\psi}(w,\texttt{t}^+,\overline{\rho})/\pi)=e(R^{\square,\psi}(w,\texttt{t}^-,\overline{\rho})/\pi),

where t\texttt{t}^- is conjugate to t+\texttt{t}^+. This proposes extending the usual Breuil–Mézard conjecture to cases not yet known in the paper; the displayed multiplicity formula is intended to relate deformation-ring special fibres to mod-pp representation-theoretic data, while the equality for conjugate types addresses the exceptional ambiguity between the two extensions.

Sources & referencesView supporting material

Primary source

Sandra Rozensztajn, “Potentially semi-stable deformation rings for discrete series extended types”, arXiv:1403.1794 (2015).

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