Operator synthesis and tensor products

Abstract

We show that Kraus' property $S_σ$ is preserved under taking weak* closed sums with masa-bimodules of finite width, and establish an intersection formula for weak* closed spans of tensor products, one of whose terms is a masa-bimodule of finite width. We initiate the study of the question of when operator synthesis is preserved under the formation of products and prove that the union of finitely many sets of the form $κ\times λ$, where $κ$ is a set of finite width, while $λ$ is operator synthetic, is, under a necessary restriction on the sets $λ$, again operator synthetic. We show that property $S_σ$ is preserved under spatial Morita subordinance. En route, we prove that non-atomic ternary masa-bimodules possess property $S_σ$ hereditarily.