Fourier-analytic cuspidal restriction conjecture for Lie algebra orbit closures

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Let FF be a local or finite field, let G\underline G be a split semisimple group with Lie algebra g\mathfrak g, and let Ωg\Omega\subset\mathfrak g be a conjugacy class with closure Ωˉ\bar\Omega. For (x,N)YΩ(x,N)\in Y^\Omega, where YΩY^\Omega consists of pairs satisfying x+NΩˉx+N\subset\bar\Omega, let fyf_y be the function on NN given by fy(n)=f(x+n)f_y(n)=f(x+n) and let f^y\hat f_y be its Fourier transform on NN^\vee. Define S(Ωˉ)cusp\mathcal S(\bar\Omega)_{cusp} as the restrictions to Ωˉ\bar\Omega of functions fS(g)f\in\mathcal S(\mathfrak g) whose Fourier transforms are supported on the elliptic set gell\mathfrak g^\vee_{ell}, and define Sw(Ωˉ)\mathcal S_w(\bar\Omega) by requiring

f^yS(Ny{0})\hat f_y\in\mathcal S(N_y^\vee\setminus\{0\})

for every y=(x,N)YΩy=(x,N)\in Y^\Omega. Fourier-analytic cuspidal restriction conjecture.

S(Ωˉ)cusp=Sw(Ωˉ).\mathcal S(\bar\Omega)_{cusp}=\mathcal S_w(\bar\Omega).

This is formulated as a Lie algebra analogue of the preceding conjecture and also makes sense for archimedean fields. For finite and non-archimedean fields, the defining Fourier-support condition is equivalent to vanishing of the integral over NyN_y, while the general assertion remains open in the source.

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Sources & referencesView supporting material

Primary source

David Kazhdan, “A question about the Fourier transform”, arXiv:2502.01230 (2025).

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