A Dolbeault complex for the contact quantised flag manifolds of type $\mathrm{C}_{2}$ and $\mathrm{D}_{4}$

Abstract

Differential calculi on non-irreducible quantised flag manifolds of the $\mathrm{A}$-series have recently been investigated using Lusztig positive root vectors, revealing that several features of classical differential geometry persist in the noncommutative setting. We extend this investigation to quantised flag manifolds associated with the lowest-rank quantum groups of types $\mathrm{C}$ and $\mathrm{D}$ whose classical spaces are holomorphic contact manifolds. Building on the Heckenberger--Kolb framework, we construct covariant first order differential calculi. The maximal prolongations of calculi restricted to contact directions have lower dimensions than their classical counterparts. In type $\mathrm{C}_2$, however, adjoining the Reeb direction yields a three-dimensional calculus on the contact flag manifold whose maximal prolongation has classical dimension. Adjoining the remaining simple-root direction yields a four-dimensional calculus on the full flag manifold, again with a maximal prolongation of classical dimension. For both calculi, we explicitly present the exterior algebras and identify them with those of the corresponding framing calculi on the quantum group. In type $\mathrm{D}_4$, we show that adjoining the Reeb direction yields a nine-dimensional calculus on the contact flag. We conjecture that its maximal prolongation also has classical dimension.