Semibounded representations of hermitian Lie groups

Abstract: A unitary representation of a, possibly infinite dimensional, Lie group $G$ is called semibounded if the corresponding operators $i\dd\pi(x)$ from the derived representation are uniformly bounded from above on some non-empty open subset of the Lie algebra $\g$ of $G$. A hermitian Lie group is a central extension of the identity component of the automorphism group of a hermitian Hilbert symmetric space. In the present paper we classify the irreducible semibounded unitary representations of hermitian Lie groups corresponding to infinite dimensional irreducible symmetric spaces. These groups come in three essentially different types: those corresponding to negatively curved spaces (the symmetric Hilbert domains), the unitary groups acting on the duals of Hilbert domains, such as the restricted Gra\ss{}mannian, and the motion groups of flat spaces.