Finite-dimensional approximations and semigroup coactions for operator algebras

TL;DR

This paper extends the concept of residual finite-dimensionality from C*-algebras to general operator algebras, introducing new tools like semigroup coactions to construct finite-dimensional approximations and exploring inheritance properties.

Contribution

It introduces the notion of residually finite-dimensional coactions for operator algebras and studies their role in finite-dimensional approximations and inheritance properties.

Findings

Constructed finite-dimensional approximations for operator algebras of functions and semigroups.

Resolved cases where residual finite-dimensionality is inherited by maximal C*-covers.

Developed novel tools for handling non-self-adjoint operator algebras.

Abstract

The residual finite-dimensionality of a $\mathrm{C}^*$-algebra is known to be encoded in a topological property of its space of representations, stating that finite-dimensional representations should be dense therein. We extend this paradigm to general (possibly non-self-adjoint) operator algebras. While numerous subtleties emerge in this greater generality, we exhibit novel tools for constructing finite-dimensional approximations. One such tool is a notion of a residually finite-dimensional coaction of a semigroup on an operator algebra, which allows us to construct finite-dimensional approximations for operator algebras of functions and operator algebras of semigroups. Our investigation is intimately related to the question of whether residual finite-dimensionality of an operator algebra is inherited by its maximal $\mathrm{C}^*$-cover, which we resolve in many cases of interest.