A Boolean action of C(M,U(1)) without a spatial model and a re-examination of the Cameron–Martin Theorem

We will demonstrate that if M is an uncountable compact metric space, then there is an action of the Polish group of all continuous functions fromM to U(1) on a separable probability algebra which preserves the measure and yet does not admit a point realization in the sense ofMackey. This is achieved by exhibiting a strong form of ergodicity of the Boolean action known as whirliness. This is in contrast with Mackey’s point realization theorem, which asserts that any measure preserving Boolean action of a locally compact second countable group on a separable probability algebra can be realized as an action on the points of the associated probability space. In the course of proving the main theorem, we will prove a result concerning the infinite-dimensional Gaussian measure space (RN,γ∞) which is in contrast with the Cameron–Martin Theorem. © 2012 Elsevier Inc. All rights reserved