Gluing parabolic character sheaves

Abstract

We introduce and study the category of unipotent character sheaves on the non-degenerate locus of the Vinberg semigroup associated to a reductive group of adjoint type. We show that appropriate perverse objects in this category can be glued from perverse parabolic character sheaves on the strata. As an application, we study the intermediate extensions of simple unipotent character sheaves from the group to its wonderful compactification, proving a conjecture of He. We also disprove a conjecture of Lusztig regarding the intermediate extension of the Steinberg character sheaf.