Generalized Ihara's lemma for unitary similitude groups

Let F=F+EF=F^+E be a CM field with E/QE/{\mathbb Q} quadratic imaginary, and let G\overline G be the associated unitary similitude group. Let SS be a finite set of places and let TS\mathbb T_S be the unramified Hecke algebra outside SS. Suppose that U\overline U is an open compact subgroup of G(A)\overline G({\mathbb A}) whose local component outside SS is maximal compact, that w0Sw_0\notin S is a place decomposed in EE, and that m\mathfrak m is a maximal ideal of TS\mathbb T_S such that the associated residual representation ρm\overline\rho_{\mathfrak m} is absolutely irreducible. Write U=Uw0Uw0\overline U=\overline U_{w_0}\overline U^{w_0}. Generalized Ihara's lemma. If πˉ\bar\pi is an irreducible subrepresentation of

C\oo(G(Q)\G(A)/Uw0,Fl)m,\mathcal C^\oo\left(\overline G({\mathbb Q})\backslash\overline G({\mathbb A})/\overline U^{w_0},\overline{\mathbb F}_l\right)_{\mathfrak m},

then its local component πˉw0\bar\pi_{w_0} at w0w_0 is generic. This is a global form of Ihara's lemma, asserting genericity of the local representation at a split unramified place under an absolute irreducibility hypothesis on the residual Galois representation; the supplied text does not indicate whether the assertion has been proved or remains open.

Sources & referencesView supporting material

Primary source

Pascal Boyer, “Local Ihara's lemma and applications”, arXiv:1810.06020 (2021).

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