Treumann–Venkatesh admissibility and functoriality conjectures for Tate cohomology

Let GG and HH be the groups occurring in the Local Langlands correspondence, let Z[[σ]\boldsymbol{Z}[[\sigma] be the group ring of σZ/Z\langle \sigma\rangle\cong \boldsymbol{Z}/\ell\boldsymbol{Z}, and let Tj(Π)\mathrm{T}^j(\Pi) denote the Tate cohomology groups of a G(E)σG(E)\rtimes\sigma-representation Π\Pi, viewed as representations of H(E)H(E). Let Π\Pi be an irreducible smooth representation of G(E)G(E) whose isomorphism class is fixed by σ\sigma, so that its G(E)G(E)-action uniquely extends to a G(E)σG(E)\rtimes\sigma-action. For each jZ/2Zj\in\mathbf{Z}/2\mathbf{Z}, two assertions are made. Treumann–Venkatesh admissibility and functoriality conjectures. First, Tj(Π)\mathrm{T}^j(\Pi) is admissible as a representation of H(E)H(E). Second, the LL-parameter of every irreducible H(E)H(E)-subquotient of Tj(Π)\mathrm{T}^j(\Pi) is sent by the σ\sigma-dual homomorphism ψˇ\check{\psi} to the LL-parameter for Π():=Πk,Frob\Pi^{(\ell)}:=\Pi\otimes_{k,\operatorname{Frob}}\ell, the Frobenius twist of Π\Pi. These conjectures propose that Tate cohomology realizes the expected representation-theoretic and LL-parameter-level compatibility in the Local Langlands Correspondence, but the supplied text gives no evidence resolving either assertion.

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Primary source

Tony Feng, “Modular functoriality in the Local Langlands Correspondence”, arXiv:2312.12542 (2024).

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