A Common Structure in PBW Bases of the Nilpotent Subalgebra of U_q(g)

Abstract

For a finite-dimensional simple Lie algebra $mathfrak{g}$, let $U^+_q(mathfrak{g})$ be the positive part of the quantized universal enveloping algebra, and $A_q(mathfrak{g})$ be the quantized algebra of functions. We show that the transition matrix of the PBW bases of $U^+_q(mathfrak{g})$ coincides with the intertwiner between the irreducible $A_q(mathfrak{g})$-modules labeled by two different reduced expressions of the longest element of the Weyl group of $mathfrak{g}$. This generalizes the earlier result by Sergeev on $A_2$ related to the tetrahedron equation and endows a new representation theoretical interpretation with the recent solution to the 3D reflection equation for $C_2$. Our proof is based on a realization of $U^+_q(mathfrak{g})$ in a quotient ring of $A_q(mathfrak{g})$.

Keywords

• quantized enveloping algebra
• PBW bases
• quantized algebra of functions
• tetrahedron equation