A Counterexample in Von Neumann Algebra Dynamics
نویسنده
چکیده
In this essay we construct a noncommutative von Neumann dynamical system with certain pathological properties from the viewpoint of analogies with classical ergodic theory. These relate to obstructions to the existence of special kinds of subsystem or subextension. We will build our example as an extension of a commutative dynamical system via a unitary cocycle acting on a Hilbert bundle, and will see that the well-known possibility of pathological behaviour for such unitary cocycles can, with a little care, be translated into pathological behaviour for von Neumann dynamical system extensions.
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