turkmath.org

We consider positive semidefinite kernels valued in the *-algebra of continuous and continuously adjointable operators on a VH-space (Vector Hilbert space in the sense of Loynes) and that are invariant under actions of *-semigroups. For such a kernel we obtain two necessary and sufficient boundedness conditions in order for there to exist *-representations of the underlying *-semigroup on a VH-space linearisation, equivalently, on a reproducing kernel VH-space. We exhibit several situations when the latter boundedness condition is automatically fulfilled.