Weakly admissible H∞−-calculus on reflexive Banach spaces

We show that, given a reflexive Banach space and a generator of an exponentially stable C0-semigroup, a weakly admissible operator g(A) can be defined for any g bounded, analytic function on the left half-plane. This yields an (unbounded) functional calculus. The construction uses a Toeplitz operator and is motivated by system theory. In separable Hilbert spaces, we even get admissibility. Furthermore, it is investigated when a bounded calculus can be guaranteed. For this we introduce the new notion of exact observability by direction.