A proof of Lusztig's conjectures for affine type $G_2$ with arbitrary parameters

TL;DR

This paper proves Lusztig's conjectures for the affine Weyl group of type G_2 with all parameters, using balanced systems of cell representations to compute the -function and analyzing Kazhdan-Lusztig cells.

Contribution

It introduces a method to compute Lusztig's -function via balanced cell representations and explicitly constructs such systems for G_2, confirming all conjectures for this case.

Findings

Confirmed Lusztig's conjectures -- for G_2 with arbitrary parameters.

Explicitly constructed balanced systems of cell representations for G_2.

Connected Kazhdan-Lusztig cells with the Plancherel Theorem, identifying Duflo involutions.

Abstract

We prove Lusztig's conjectures ${\bf P1}$--${\bf P15}$ for the affine Weyl group of type $\tilde{G}_2$ for all choices of parameters. Our approach to compute Lusztig's $\mathbf{a}$-function is based on the notion of a "balanced system of cell representations" for the Hecke algebra. We show that for arbitrary Coxeter type the existence of balanced system of cell representations is sufficient to compute the $\mathbf{a}$-function and we explicitly construct such a system in type $\tilde{G}_2$ for arbitrary parameters. We then investigate the connection between Kazhdan-Lusztig cells and the Plancherel Theorem in type $\tilde{G}_2$, allowing us to prove ${\bf P1}$ and determine the set of Duflo involutions. From there, the proof of the remaining conjectures follows very naturally, essentially from the combinatorics of Weyl characters of types $G_2$ and $A_1$, along with some explicit computations for the finite cells.