Clozel–Harris–Taylor's generalized Ihara lemma for definite unitary groups

Let F+\mathsf{F}^+ be a totally real number field, let F/F+\mathsf{F}/\mathsf{F}^+ be a quadratic CM extension containing an imaginary quadratic field K\mathsf{K}, and let G\mathsf{G} be the unitary similitude group associated to a division algebra with involution as in the setup. At a prime pp split in K\mathsf{K}, choose a place vv of F\mathsf{F} above a fixed place \wp of K\mathsf{K} above pp, with the division algebra split at vv. Let KvK^v and A(Kv)\mathcal{A}(K^v) be as defined above, let Λ=F\Lambda=\overline{\mathbb{F}}_\ell for p\ell\neq p, and let TS\mathbb{T}^S be the global Hecke algebra. An irreducible GLn(Fv)\mathrm{GL}_n(\mathsf{F}_v)-representation over Λ\Lambda is Whittaker-generic if it admits nonzero Whittaker coefficients. Let mTS\mathfrak{m}\subseteq\mathbb{T}^S be a non-Eisenstein maximal ideal with A(Kv)m0\mathcal{A}(K^v)_\mathfrak{m}\neq 0, and let VA(Kv)mV\subseteq\mathcal{A}(K^v)_\mathfrak{m} be an irreducible GLn(Fv)\mathrm{GL}_n(\mathsf{F}_v)-submodule.

Clozel–Harris–Taylor's generalized Ihara lemma. Then VV is Whittaker-generic.

This is the generalized Ihara lemma proposed by Clozel, Harris, and Taylor for higher-dimensional unitary groups. The supplied material does not state whether this formulation has been proved or remains open.

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Primary source

Xiangqian Yang, “On Ihara's lemma for definite unitary groups”, arXiv:2504.07504 (2025).

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