Complete Boolean algebras of type I factors

Abstract

A partial classification into unitary equivalence classes of complete Boolean algebras of type I factors is given. Any complete atomic Boolean algebra of type I factors is unitarily equivalent to a discrete tensor product of type I factors. We establish a one-to-one correspondence between the unitary equivalence classes of complete nonatomic Boolean algebras of type I factors satisfying a certain condition, and the unitary equivalence classes of complete nonatomic Boolean algebras of projections. A continuous tensor product of Hilbert spaces is defined which is a generalization of the discrete infinite incomplete tensor product space defined by von Neumann. On a separable Hilbert space, any complete nonatomic Boolean algebra of type I factors satisfying the previously mentioned condition is unitarily equivalent to a continuous tensor product of type I factors. An application to the representations of the canonical commutation relations of quantum field theory is made.