Conjectural presentation of the tamely ramified Eisenstein module

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Let GG be a reductive group satisfying the stated restriction that, for every root αˇ∈Λ∨\check{\alpha}\in\Lambda^{\vee}, the map Λ→Z\Lambda\to\mathbb{Z} given by λ↦⟨αˇ,λ⟩\lambda\mapsto\langle\check{\alpha},\lambda\rangle is surjective. Let S={0,1,∞}S=\{0,1,\infty\} be the ramification points, let H⊗S\mathcal{H}^{\otimes S} be the algebra generated by the Hecke operators at the points of SS, and let CEisC_{Eis} be the module of tamely ramified Eisenstein series. For λ∈Λ\lambda\in\Lambda, write JλsJ_\lambda^s for the corresponding translation Hecke operator at s∈Ss\in S, and for a simple reflection sα∈Ws_\alpha\in W, write TsαsT_{s_\alpha}^s for the corresponding Hecke operator at ss. Conjectural presentation. The module CEisC_{Eis} is generated as an H⊗S\mathcal{H}^{\otimes S}-module by Eis0\mathrm{Eis}_0, subject to the relations

Jλ0Eis0=Jλ1Eis0=Jλ∞Eis0J_{\lambda}^0\mathrm{Eis}_0=J_{\lambda}^1\mathrm{Eis}_0=J_{\lambda}^{\infty}\mathrm{Eis}_0

for every λ∈Λ\lambda\in\Lambda, and

(1+Tsα0)(1+Tsα1)Eis0=(1+Tsα0)(1+Tsα∞)Eis0=(1+Tsα1)(1+Tsα∞)Eis0(1+T_{s_\alpha}^0)(1+T_{s_\alpha}^1)\mathrm{Eis}_0=(1+T_{s_\alpha}^0)(1+T_{s_\alpha}^{\infty})\mathrm{Eis}_0=(1+T_{s_\alpha}^1)(1+T_{s_\alpha}^{\infty})\mathrm{Eis}_0

for every simple reflection sα∈Ws_\alpha\in W. This would give an explicit presentation of the Hecke module generated by the unramified Eisenstein series and describe the relations imposed by translations and simple reflections; the supplied text does not indicate that the conjecture has been proved or disproved.

References

Primary source

Tahsin Saffat, “Hecke action on tamely ramified Eisenstein series over P^1”, arXiv:2309.11085 (2023).

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