Ihara's lemma for unitary groups

Let GG be the unitary group and retain the paper's notation for the coefficient system Sa,{ρx},S_{a,\{\rho_x\},\varnothing}, the set of places TT, and the level subgroup UU. A place vv is banal in the sense used in the paper, and UvU^v denotes the corresponding level modification. Let kˉ\bar{k} be the residue field, and call a maximal ideal non-Eisenstein when its associated residual representation rˉm\bar{r}_{\mathfrak m} is absolutely irreducible. Ihara's lemma. Let UG(AF+)U\subset G(\mathbb A_{F^+}^{\infty}) be sufficiently small, let vT(SS(B))v\in T-(S_{\ell}\cup S(B)) be a place where Uv=G(OFv+)U_v=G(\mathcal O_{F_v^+}), let mTa,{ρx},T(U)\mathfrak m\subset\mathbb T_{a,\{\rho_x\},\varnothing}^T(U) be a non-Eisenstein maximal ideal, and let fSa,{ρx},(U,kˉ)[m]f\in S_{a,\{\rho_x\},\varnothing}(U,\bar{k})[\mathfrak m] be an eigenform. Then every irreducible kˉ[G(Fv+)]\bar{k}[G(F_v^+)]-submodule π\pi satisfying

πG(Fv+)fSa,{ρx},(Uv,kˉ)\pi\subset\langle G(F_v^+)f\rangle\subset S_{a,\{\rho_x\},\varnothing}(U^v,\bar{k})

is generic. This is the Ihara-lemma input for the non-minimal modularity-lifting argument; the paper notes that it follows from the trivial-data case, but treats the assertion as conjectural here.

Sources & referencesView supporting material

Primary source

Claus Sorensen, “The local Langlands correspondence in families and Ihara's lemma for U(n)”, arXiv:1406.1830 (2014).

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