Parabolic Kazhdan-Lusztig basis, Schubert classes, and equivariant oriented cohomology

TL;DR

This paper explores the structure of equivariant oriented cohomology rings of partial flag varieties, introduces a new interpretation of parabolic Kazhdan-Lusztig bases, and discusses positivity and smoothness conjectures with partial proofs.

Contribution

It provides a new interpretation of parabolic Kazhdan-Lusztig bases and defines KL Schubert classes independently of reduced words, extending previous work.

Findings

Bott-Samelson classes obtained via Hecke action on the fundamental class.

New interpretation of Deodhar's construction of parabolic KL basis.

Partial proofs of positivity and smoothness conjectures.

Abstract

We study the equivariant oriented cohomology ring $h_T(G/P)$ of partial flag varieties using the moment map approach. We define the right Hecke action on this cohomology ring, and then prove that the respective Bott-Samelson classes in $h_{T}(G/P)$ can be obtained by applying this action to the fundamental class of the identity point, hence generalizing previously known results by Brion, Knutson, Peterson, Tymoczko and others. We then focus on the equivariant oriented cohomology theory corresponding to the 2-parameter Todd genus. We give a new interpretation of Deodhar's construction of the parabolic Kazhdan-Lusztig basis. Based on it, we define the parabolic Kazhdan-Lusztig (KL) Schubert classes independently of a reduced word. We make a positivity conjecture, and a conjecture about the relationship of such classes with smoothness of Schubert varieties. We then prove several special cases.