Relating Signed Kazhdan-Lusztig Polynomials and Classical Kazhdan-Lusztig Polynomials

Abstract

Motivated by studying the Unitary Dual Problem, a variation of Kazhdan-Lusztig polynomials was defined in [Yee08] which encodes signature information at each level of the Jantzen filtration. These so called signed Kazhdan-Lusztig polynomials may be used to compute the signatures of invariant Hermitian forms on irreducible highest weight modules. The key result of this paper is a simple relationship between signed Kazhdan-Lusztig polynomials and classical Kazhdan-Lusztig polynomials: signed Kahzdan-Lusztig polynomials are shown to equal classical Kazhdan-Lusztig polynomials evaluated at $-q$ rather than $q$ and multiplied by a sign. This result has applications to finding the unitary dual for real reductive Lie groups since Harish-Chandra modules may be constructed by applying Zuckerman functors to highest weight modules.