Heisenberg parabolically induced representations of Hermitian Lie groups, Part I: Unitarity and subrepresentations

For a Hermitian Lie group $G$, we study the family of representations induced from a character of the maximal parabolic subgroup $P=MAN$ whose unipotent radical $N$ is a Heisenberg group. Realizing these representations in the non-compact picture on a space $I(\nu )$ of functions on the opposite unipotent radical $\bar{N}$, we apply the Heisenberg group Fourier transform mapping functions on $\bar{N}$ to operators on Fock spaces. The main result is an explicit expression for the Knapp-Stein intertwining operators $I(\nu )\to I(-\nu )$ on the Fourier transformed side. This gives a new construction of the complementary series and of certain unitarizable subrepresentations at points of reducibility. Further auxiliary results are a Bernstein-Sato identity for the Knapp-Stein kernel on $\bar{N}$ and the decomposition of the metaplectic representation under the non-compact group $M$.