Graded Hecke algebras, constructible sheaves and the p-adic Kazhdan--Lusztig conjecture

Abstract

Graded Hecke algebras can be constructed in terms of equivariant cohomology and constructible sheaves on nilpotent cones. In earlier work, their standard modules and their irreducible modules where realized with such geometric methods. We pursue this setup to study properties of module categories of (twisted) graded Hecke algebras, in particular what happens geometrically upon formal completion with respect to a central character. We prove a version of the Kazhdan--Lusztig conjecture for (twisted) graded Hecke algebras. It expresses the multiplicity of an irreducible module in a standard module as the multiplicity of an equivariant local system in an equivariant perverse sheaf. This is applied to smooth representations of reductive p-adic groups. Under some conditions, we verify the p-adic Kazhdan--Lusztig conjecture from [Vogan]. Here the equivariant constructible sheaves live on certain varieties of Langlands parameters. The involved conditions are checked for substantial classes of groups and representations.