Refined local Langlands compatibility conjecture for restriction and induction

Let G\overline{G} be a covering group with subgroup G0\overline{G}_0, let G=Z(G)G0\overline{G}^\dag=\overline{Z(G)}\cdot\overline{G}_0, and let ϕπ\phi_\pi be an LL-parameter of G\overline{G}. Write ϕπ=fG,Hϕπ\phi_\pi^\diamondsuit=f_{G,H}\circ\phi_\pi and let Φ(LG0;ϕπ)\Phi({}^L\overline{G}_0;\phi_\pi) be the set of parameters ϕ0\phi_0 satisfying fG0,Hϕ0=ϕπf_{G_0,H}\circ\phi_0=\phi_\pi^\diamondsuit. For enhanced parameters (ϕ,θ)(\phi,\theta), write Sϕ\mathcal{S}_\phi for the component group and use the embeddings into Sϕπ\mathcal{S}_{\phi_\pi^\diamondsuit}. Let πIrrgen(G)\pi\in\operatorname{Irr}_{\rm gen}(\overline{G}) have central character ωπ\omega_\pi and enhanced parameter (ϕπ,θπ)(\phi_\pi,\theta_\pi), and let τρ\tau\boxtimes\rho be an irreducible constituent of πG\pi|_{\overline{G}^\dag}. Restriction and induction compatibility conjecture. (i) The parameters satisfy fG,zϕπ=fc,zϕτ=ϕωπf_{G,z}\circ\phi_\pi=f_{c,z}\circ\phi_\tau=\phi_{\omega_\pi} and ϕπ=fG0,Hϕρ\phi_\pi^\diamondsuit=f_{G_0,H}\circ\phi_\rho. (ii) There exists e(π)Ne(\pi)\in\mathbf{N} such that for every τIrrgen(G0)\tau\in\operatorname{Irr}_{\rm gen}(\overline{G}_0) with enhanced parameter (ϕτ,θτ)(\phi_\tau,\theta_\tau),

dimHomG0(π,τ)={0if ϕτΦ(LG0;ϕπ),e(π)IndSϕπSϕπθπ,IndSϕτSϕπθτSϕπif ϕτΦ(LG0;ϕπ).\dim\operatorname{Hom}_{\overline{G}_0}(\pi,\tau)=\begin{cases}0&\text{if }\phi_\tau\notin\Phi({}^L\overline{G}_0;\phi_\pi),\\ e(\pi)\left\langle\operatorname{Ind}_{\mathcal{S}_{\phi_\pi}}^{\mathcal{S}_{\phi_\pi^\diamondsuit}}\theta_\pi,\operatorname{Ind}_{\mathcal{S}_{\phi_\tau}}^{\mathcal{S}_{\phi_\pi^\diamondsuit}}\theta_\tau\right\rangle_{\mathcal{S}_{\phi_\pi^\diamondsuit}}&\text{if }\phi_\tau\in\Phi({}^L\overline{G}_0;\phi_\pi).\end{cases}

In the isotypic case, the stated direct-sum formula for πG0\pi|_{\overline{G}_0} holds. (iii) Compatible τIrrgen(Z(G))\tau\in\operatorname{Irr}_{\rm gen}(\overline{Z(G)}) and ρIrrgen(G0)\rho\in\operatorname{Irr}_{\rm gen}(\overline{G}_0) induce constituents whose parameters fit into the specified commutative LL-group diagram. This conjectural package predicts compatibility of enhanced local Langlands parameters with central characters, restriction, and induction.

Sources & referencesView supporting material

Primary source

Fan Gao, Freydoon Shahidi and Dani Szpruch, “Restrictions, L-parameters, and local coefficients for genuine representations”, arXiv:2102.08859 (2021).

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