Steinberg quotients, Weyl characters, and Kazhdan-Lusztig polynomials

Abstract

Let G G be a reductive group over a field of prime characteristic. An indecomposable tilting module for G G whose highest weight lies above the Steinberg weight has a character that is divisible by the Steinberg character. The resulting “Steinberg quotient” carries important information about G G -modules, and in previous work we studied patterns in the weight multiplicities of these characters. In this paper we broaden our scope to include quantum Steinberg quotients, and show how the multiplicities in these characters relate to algebraic Steinberg quotients, Weyl characters, and evaluations of Kazhdan-Lusztig polynomials. We give an explicit algorithm for computing minimal characters that possess a key attribute of Steinberg quotients. We provide computations which show that these minimal characters are not always equal to quantum Steinberg quotients, but are close in several nontrivial cases.