We prove some structure results for isometries between noncommutative L spaces associated to von Neumann algebras. We find that an isometry T : L(M1) → L(M2) (1 ≤ p < ∞, p 6= 2) can be canonically expressed in a certain simple form whenever M1 has variants of Watanabe’s extension property [W2]. Conversely, this form always defines an isometry provided that M1 is “approximately semifinite” (defi...

Let %? be a separable Hubert space and !T c 3§(J%f) be an algebra of bounded operators. Say F is triangular if ^ n ^ * is a maximal abelian self-adjoint subalgebra (m.a.s.a.) of 3B{%?) and call this m.a.s.a. the diagonal of J7". A triangular algebra is maximal triangular if it is not properly contained in any triangular algebra. Triangular algebras of operators have been studied for 30 years no...

In this fourth of our series of papers on observables we show that one can associate to each von Neumann algebra R a pair of isomorphic presheaves, the upper presheaf O Rand the lower presheaf O − R , on the category of abelian von Neumann subalgebras of R. Each A ∈ Rsa induces a global section of O R and of O − R respectively. We call them contextual observables. But we show that, in general, ...

It is well known in the work of Kadison and Ringrose 1983 that if A and B are maximal abelian von Neumann subalgebras of von Neumann algebras M and N, respectively, then A⊗B is a maximal abelian von Neumann subalgebra of M⊗N. It is then natural to ask whether a similar result holds in the context of JW-algebras and the JW-tensor product. Guided to some extent by the close relationship between a...

We review topologic properties of orbits of states of von Neumann algebras, starting with unitary orbits, and proceeding with more general sets of states, namely vector states with symbol a spheric vector in a Hilbert C∗module of the algebra. This is done by considering natural bundles over these sets, which enable one to relate their topologic properties to those of the unitary groups of von N...

There is a Banach algebra satisfying the von Neumann inequality for polynomials in a single variable, without constant term, which is not isomorphic to a norm-closed algebra of operators on a Hilbert space.

By improving the previous construction in [18] we observe that any reduced HNN extension is a corner of a certain reduced amalgamated free product in both the von Neumann algebra and the C∗-algebra settings. Then, the same fact is shown for universal HNN extensions of C∗-algebras. We apply the observation to the questions of factoriality and type classification of HNN extensions of von Neumann ...

In a previous paper, we showed that every strongly commuting pair of CP0-semigroups on a von Neumann algebra (acting on a separable Hilbert space) has an E0-dilation. In this paper we show that if one restricts attention to the von Neumann algebra B(H) then the unitality assumption can be dropped, that is, we prove that every pair of strongly commuting CP-semigroups on B(H) has an E-dilation. T...

In this note we include two remarks about bounded (not necessarily contractive) linear projections on a von Neumann-algebra. We show that if M is a von Neumann-subalgebra of B(H) which is complemented in B(H) and isomorphic to M ⊗ M then M is injective (or equivalently M is contractively complemented). We do not know how to get rid of the second assumption on M. In the second part,we show that ...

form the base of a topology on the Stone spectrum Q(R) such that Q(R) becomes a zero-dimensional, completely regular Hausdorff space. The sets QP (R) are closed-open. If the von Neumann algebra R is abelian, then the Stone spectrum Q(R) is homeomorphic to the Gelfand spectrum Ω(R) of R. For an arbitrary non-abelian unital von Neumann algebra R, the Stone spectrum can hence be regarded as a non-...