The wavefront set: bounds for the Langlands parameter

Abstract

For an irreducible smooth representation of a connected reductive $p$-adic group, two important associated invariants are the wavefront set and the (partly conjectural) Langlands parameter. While a wavefront set consists of $p$-adic nilpotent orbits, one constituent of the Langlands parameter is a complex nilpotent orbit in the dual Lie algebra. For unipotent representations in the sense of Lusztig, the corresponding nilpotent orbits on the two sides are related via the Lusztig--Spaltenstein duality, by the work of Ciubotaru--Mason-Brown--Okada. In this paper, we formulate a general upper-bound conjecture and several variants relating the nilpotent orbits that appear in the wavefront set and in the Langlands parameter. We also verify these expectations in some cases, including the depth-zero supercuspidal representations of classical groups and all the irreducible representations of $G_2$.

22 pages; v2: expanded the section on G2 to include all tempered L-packets, added remarks in the introduction, additional references, corrections; v3: added details for the calculation of the Spaltenstein duality, and fully verified the conjectures in the case of G2