Cotangent-case Borel-orbit duality conjecture

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Let GG be a reductive group with Langlands dual group G∨G^\vee, and let WW be the Weyl group. Let XX be a smooth spherical GG-variety such that T∗XT^*X is hyperspherical and has relative Langlands dual of the form T∗X∨T^*X^\vee for a smooth spherical G∨G^\vee-variety X∨X^\vee. Let B\XB\backslash X and B∨\X∨B^\vee\backslash X^\vee denote the sets of Borel orbits, and let rank⁡(Y)\operatorname{rank}(Y) denote the dimension of the lattice of BB-semi-invariant rational-function characters on a variety YY. Cotangent-case orbit-duality conjecture. There exists a bijection

Φ:B\X⟶B∨\X∨\Phi:B\backslash X\longrightarrow B^\vee\backslash X^\vee

that intertwines Knop's Weyl-group action and satisfies rank⁡(x)+rank⁡(Φ(x))=rank⁡(G)\operatorname{rank}(x)+\operatorname{rank}(\Phi(x))=\operatorname{rank}(G). For every simple reflection s∈Ws\in W, an orbit x∈B\Xx\in B\backslash X has type GG with respect to ss if and only if Φ(x)\Phi(x) has type T2T2 with respect to ss, and conversely.

This conjecture translates the relative Langlands duality prediction into combinatorics of Borel orbits. The source proposes it based on computations used in proving the main theorem; no resolution is given.

References

Primary source

Guy Kapon and Guy Shtotland, “On Representations of Weyl Groups attached to Spherical Varieties”, arXiv:2607.24108 (2026).

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