The depth inequality and equality conjecture for Langlands packets

Let GG be a connected reductive group over FF that splits over FtF^t, let φ\varphi be a positive-depth Langlands parameter for G(F)G(F), and let Π(φ)\Pi(\varphi) be its associated LL-packet. Write ρ(φ)\rho(\varphi) for the depth of φ\varphi and ρ(π)\rho(\pi) for the depth of a representation π\pi. Depth conjecture. For every πΠ(φ)\pi\in\Pi(\varphi),

ρ(φ)ρ(π).\rho(\varphi)\leq\rho(\pi).

If pp does not divide the order of the absolute Weyl group of GG, then

ρ(φ)=ρ(π).\rho(\varphi)=\rho(\pi).

The conjecture is motivated by known equalities and inequalities for several classes of groups, together with examples where the inequality is strict; the source gives no general proof or disproof.

Sources & referencesView supporting material

Primary source

Tsao-Hsien Chen, Stephen DeBacker and Cheng-Chiang Tsai, “Langlands parameters for Moy-Prasad types”, arXiv:2509.07780 (2025).

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