Positivity conjectures for Kazhdan-Lusztig theory on twisted involutions: the finite case

Abstract

Let $(W,S)$ be any Coxeter system and let $w \mapsto w^*$ be an involution of $W$ which preserves the set of simple generators $S$. Lusztig and Vogan have shown that the corresponding set of twisted involutions (i.e., elements $w \in W$ with $w^{-1} = w^*$) naturally generates a module of the Hecke algebra of $(W,S)$ with two distinguished bases. The transition matrix between these bases defines a family of polynomials $P^σ_{y,w}$ which one can view as a "twisted" analogue of the much-studied family of Kazhdan-Lusztig polynomials of $(W,S)$. The polynomials $P^σ_{y,w}$ can have negative coefficients, but display several conjectural positivity properties of interest, which parallel positivity properties of the Kazhdan-Lusztig polynomials. This paper reports on some calculations which verify four such positivity conjectures in several finite cases of interest, in particular for the non-crystallographic Coxeter systems of types $H_3$ and $H_4$.

24 pages, 3 tables; v2: material signficantly condensed, some minor corrections and reference updates, final version