Depth-zero base change compatibility for unramified extensions

Let FF be a local field, let E/FE/F be an unramified extension, and let G\underline{G} be a reductive group over FF. For a point xx in the building of G(F)\underline{G}(F), let GxG_x be the associated parahoric subgroup and let Gx\underline{\mathsf{G}}_x be its connected reductive quotient over the residue field kFk_F. Write G~x\widetilde{G}_x for the corresponding parahoric subgroup of ResE/FG(F)=G(E)\operatorname{Res}_{E/F}\underline{G}(F)=\underline{G}(E). A representation has depth zero if it contains (Gx,infl(σ))(G_x,\operatorname{infl}(\sigma)) for an irreducible cuspidal representation σ\sigma of Gx(kF)\underline{\mathsf{G}}_x(k_F). Depth-zero base change compatibility. Suppose there is a base change lifting BCE/F\operatorname{BC}_{E/F} taking LL-packets for G(F)\underline{G}(F) to LL-packets for G(E)\underline{G}(E). If Π\Pi is a depth-zero LL-packet for G(F)\underline{G}(F), πΠ\pi\in\Pi contains (Gx,infl(σ))(G_x,\operatorname{infl}(\sigma)), and σ\sigma is irreducible and cuspidal, then some π~BCE/F(Π)\widetilde{\pi}\in\operatorname{BC}_{E/F}(\Pi) contains

(G~x,infl(BCkE/kF(σ))).(\widetilde{G}_x,\operatorname{infl}(\operatorname{BC}_{k_E/k_F}(\sigma))).

Here BCkE/kF\operatorname{BC}_{k_E/k_F} is the base change lifting associated with kE/kFk_E/k_F and the kFk_F-group Gx\underline{\mathsf{G}}_x. This conjecture expresses compatibility between base change for depth-zero representations and base change for the corresponding finite reductive groups. It is known, under additional hypotheses, for unramified quadratic extensions and unitary groups in two or three variables; the general assertion remains open.

Sources & referencesView supporting material

Primary source

Jeffrey D. Adler and Joshua M. Lansky, “Depth-zero base change for ramified U(2,1)”, arXiv:0807.1528 (2009).

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