Prasad's multiplicity formula for Galois distinction

Let E/FE/F be a quadratic extension with nontrivial Galois element σ\sigma. Let GG be a reductive group over FF, let G(E)G(E) be its base change, and let GopG^{\mathrm{op}} be the quasi-split FF-form of GG with Gop(E)G(E)G^{\mathrm{op}}(E)\cong G(E). For a regular supercuspidal representation π\pi of G(E)G(E) with Langlands–Vogan parameter (ϕπ,λπ)(\phi_\pi,\lambda_\pi), write Sϕπ=CG^(Imϕπ)S_{\phi_\pi}=C_{\widehat G}(\operatorname{Im}\phi_\pi). For each αH1(Gal(E/F),G(E))\alpha\in H^1(\operatorname{Gal}(E/F),G(E)), let GαG_\alpha be the corresponding inner form, and let ωGα(F),E\omega_{G_\alpha(F),E} be Prasad's quadratic character. For a lift ϕ~:WFLGop\widetilde\phi:W_F\to{}^LG^{\mathrm{op}} with ϕ~WE=ϕπ\widetilde\phi|_{W_E}=\phi_\pi, let m(λπ,ϕ~)m(\lambda_\pi,\widetilde\phi) be the multiplicity of the trivial representation in λππ0(Sϕ~)\lambda_\pi|_{\pi_0(S_{\widetilde\phi})}. Prasad's multiplicity formula. One has

αH1(Gal(E/F),G(E))dimHomGα(F)(π,ωGα(F),E)=ϕ~m(λπ,ϕ~),\sum_{\alpha\in H^1(\operatorname{Gal}(E/F),G(E))}\dim\operatorname{Hom}_{G_\alpha(F)}(\pi,\omega_{G_\alpha(F),E})=\sum_{\widetilde\phi}m(\lambda_\pi,\widetilde\phi),

where the right-hand sum is over all such lifts ϕ~\widetilde\phi. This is the regular-supercuspidal form of Prasad's conjecture on Galois distinction and base change; the supplied text does not state whether it has been proved in this generality.

Sources & referencesView supporting material

Primary source

Chuijia Wang, “Distinction and quadratic base change for regular supercuspidal representations”, arXiv:2201.00447 (2022).

Additional references

5 papers in this index state this conjecture (2015–2022). The statement above is taken from the most recent of them; the others are arXiv:1905.07928, arXiv:1605.00744, arXiv:1602.01297, arXiv:1502.03528.

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