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Fourier Spaces and Completely Isometric Representations of Arens Product Algebras

Part of: Linear spaces and algebras of operators Topological algebras, normed rings and algebras, Banach algebras Abstract harmonic analysis

Published online by Cambridge University Press:  07 January 2019

Ross Stokke
Ross Stokke*
Affiliation:
Department of Mathematics and Statistics, University of Winnipeg, Winnipeg, MB R3B 2E9, Canada Email: [email protected]
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Abstract

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Motivated by the definition of a semigroup compactication of a locally compact group and a large collection of examples, we introduce the notion of an (operator) homogeneous left dual Banach algebra (HLDBA) over a (completely contractive) Banach algebra $A$. We prove a Gelfand-type representation theorem showing that every HLDBA over A has a concrete realization as an (operator) homogeneous left Arens product algebra: the dual of a subspace of $A^{\ast }$ with a compatible (matrix) norm and a type of left Arens product $\Box$. Examples include all left Arens product algebras over $A$, but also, when $A$ is the group algebra of a locally compact group, the dual of its Fourier algebra. Beginning with any (completely) contractive (operator) $A$-module action $Q$ on a space $X$, we introduce the (operator) Fourier space $({\mathcal{F}}_{Q}(A^{\ast }),\Vert \cdot \Vert _{Q})$ and prove that $({\mathcal{F}}_{Q}(A^{\ast })^{\ast },\Box )$ is the unique (operator) HLDBA over $A$ for which there is a weak$^{\ast }$-continuous completely isometric representation as completely bounded operators on $X^{\ast }$ extending the dual module representation. Applying our theory to several examples of (completely contractive) Banach algebras $A$ and module operations, we provide new characterizations of familiar HLDBAs over A and we recover, and often extend, some (completely) isometric representation theorems concerning these HLDBAs.

Keywords

Banach algebraoperator spaceArens productgroup algebraFourier algebra

MSC classification

Primary: 47L10: Algebras of operators on Banach spaces and other topological linear spaces
Secondary: 43A20: $L^1$-algebras on groups, semigroups, etc. 43A30: Fourier and Fourier-Stieltjes transforms on nonabelian groups and on semigroups, etc. 46H15: Representations of topological algebras 46H25: Normed modules and Banach modules, topological modules (if not placed in or ) 47L25: Operator spaces (= matricially normed spaces)
Type
Article
Information
Canadian Journal of Mathematics , Volume 71 , Issue 3 , June 2019 , pp. 717 - 747
Copyright
© Canadian Mathematical Society 2018 

Footnotes

This research was partially supported by an NSERC grant.

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