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arXiv · 0909.3479

Wandering vectors and the reflexivity of free semigroup algebras

Matthew Kennedy
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Abstract

A free semigroup algebra S is the weak-operator-closed (non-self-adjoint) operator algebra generated by n isometries with pairwise orthogonal ranges. A unit vector x is said to be wandering for S if the set of images of x under non-commuting words in the generators of S is orthonormal. We establish the following dichotomy: either a free semigroup algebra has a wandering vector, or it is a von Neumann algebra. Consequences include that every free semigroup algebra is reflexive, and that certain free semigroup algebras are hyper-reflexive with a very small hyper-reflexivity constant.

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Matthew Kennedy. 2009-09-18. Wandering vectors and the reflexivity of free semigroup algebras. https://arxiv.org/abs/0909.3479

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