Depth-zero base change compatibility for tamely ramified extensions

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Let FF be a local field, let E/FE/F be a cyclic tamely ramified 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 and G~x\widetilde{G}_x be the corresponding parahoric subgroups, with connected reductive quotients G‾x\underline{\mathsf{G}}_x and G‾~x\widetilde{\underline{\mathsf{G}}}_x over kFk_F. If π\pi contains (Gx,infl⁡(σ))(G_x,\operatorname{infl}(\sigma)), where σ\sigma is an irreducible cuspidal representation of G‾x(kF)\underline{\mathsf{G}}_x(k_F), Depth-zero base change compatibility for tame ramification. Suppose there is a base change lifting BC⁡E/F\operatorname{BC}_{E/F} taking LL-packets for G‾(F)\underline{G}(F) to LL-packets for G‾(E)\underline{G}(E). For every depth-zero LL-packet Π\Pi for G‾(F)\underline{G}(F) and π∈Π\pi\in\Pi containing (Gx,infl⁡(σ))(G_x,\operatorname{infl}(\sigma)), some π~∈BC⁡E/F(Π)\widetilde{\pi}\in\operatorname{BC}_{E/F}(\Pi) contains

(G~x,infl⁡(σ~))(\widetilde{G}_x,\operatorname{infl}(\widetilde{\sigma}))

for some irreducible representation σ~\widetilde{\sigma} of G‾~x(kF)\widetilde{\underline{\mathsf{G}}}_x(k_F) contained in ℓ(σ)\ell(\sigma). The assertion proposes a finite-group compatibility even though the reductive quotient need not be obtained by restriction of scalars in the ramified case. The source gives no resolution status for this broader conjecture, so it is recorded as open.

References

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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