Barchini, Kable, and Zierau
constructed a number of conformally invariant systems of differential operators
associated to Heisenberg parabolic subalgebras in simple Lie algebras. The
construction was systematic, but the existence of such a system was left open in two
cases, namely, the Ω3 system for type A2 and type D4. Here, such a system is
shown to exist for both cases. The construction of the system may also be
interpreted as giving an explicit homomorphism between generalized Verma
modules.
Keywords
intertwining differential operator, generalized Verma
module, real flag manifold