Lusztig's Quantum Root Vectors and a Dolbeault Complex for the A-Series Full Quantum Flag Manifolds

Abstract

For the Drinfeld-Jimbo quantum enveloping algebra $U_q(\frak{sl}_{n+1})$, we show that the span of Lusztig's positive root vectors, with respect to Littlemann's nice reduced decompositions of the longest element of the Weyl group, form quantum tangent spaces for the full quantum flag manifold $\mathcal{O}_q(\mathrm{F}_{n+1})$. The associated differential calculi are direct $q$-deformations of the anti-holomorphic Dolbeault complex of the classical full flag manifold $\mathrm{F}_{n+1}$. As an application we establish a quantum Borel-Weil theorem for the $A_n$-series full quantum flag manifold, giving a noncommutative differential geometric realisation of all the finite-dimensional type-$1$ irreducible representations of $U_q(\frak{sl}_{n+1})$. Restricting this differential calculus to the quantum Grassmannians is shown to reproduce the celebrated Heckenberger-Kolb anti-holomorphic Dolbeault complex. Lusztig's positive root vectors for non-nice decompositions of the longest element of the Weyl group are examined for low orders, and are exhibited to either not give tangents spaces, or to produce differential calculi of non-classical dimension.