Derivations of Murray-von Neumann Algebras

  • Richard V. Kadison
  • Zhe Liu

Abstract

A Murray-von Neumann algebra is the algebra of operators affiliated with a finite von Neumann algebra. In this article, we study derivations of Murray-von Neumann algebras and their properties. We show that the "extended derivations" of a Murray-von Neumann algebra, those that map the associated finite von Neumann algebra into itself, are inner. In particular, we prove that the only derivation that maps a Murray-von Neumann algebra associated with a von Neumann algebra of type ${\rm II}_1$ into that von Neumann algebra is 0. This result is an extension, in two ways, of Singer's seminal result answering a question of Kaplansky, as applied to von Neumann algebras: the algebra may be non-commutative and contain unbounded elements. In another sense, as we indicate in the introduction, all the derivation results including ours extend what Singer's result says, that the derivation is the 0-mapping, numerically in our main theorem and cohomologically in our theorem on extended derivations. The cohomology in this case is the Hochschild cohomology for associative algebras.
Published
2014-12-03
How to Cite
Kadison, R. V., & Liu, Z. (2014). Derivations of Murray-von Neumann Algebras. MATHEMATICA SCANDINAVICA, 115(2), 206-228. https://doi.org/10.7146/math.scand.a-19223
Section
Articles