Quantum Schur-Weyl duality and projected canonical bases

TL;DR

This paper explores the relationships between different Kazhdan-Lusztig bases of Hecke algebra modules, using quantum Schur-Weyl duality to analyze transition matrices and conjecture positivity properties.

Contribution

It introduces a novel approach to compare Kazhdan-Lusztig bases via transition matrices using quantum Schur-Weyl duality and projected canonical bases.

Findings

Transition matrix S(λ) is identity at u=0 and u=∞.

Proved property for transition matrices between bases and their projected counterparts.

Conjecture on positivity of entries of S(λ).

Abstract

Let \H_r be the generic type A Hecke algebra defined over \ZZ[u, u^{-1}]. The Kazhdan-Lusztig bases \{C_w\}_{w \in \S_r} and \{C'_w\}_{w \in \S_r} of \H_r give rise to two different bases of the Specht module M_\lambda, \lambda \vdash r, of \H_r. These bases are not equivalent and we show that the transition matrix S(\lambda) between the two is the identity at u = 0 and u = \infty. To prove this, we first prove a similar property for the transition matrices \tilde{T}, \tilde{T}' between the Kazhdan-Lusztig bases and their projected counterparts \{\tilde{C}_w\}_{w \in \S_r}, \{\tilde{C}'_w\}_{w \in \S_r}, where \tilde{C}_w := C_w p_\lambda, \tilde{C}'_w := C'_w p_\lambda and p_\lambda is the minimal central idempotent corresponding to the two-sided cell containing w. We prove this property of \tilde{T},\tilde{T}' using quantum Schur-Weyl duality and results about the upper and lower canonical basis of V^{\tsr r} (V the natural representation of U_q(\gl_n)) from \cite{GL, FKK, Brundan}. We also conjecture that the entries of S(\lambda) have a certain positivity property.