Banach algebras generated by an invertible isometry of an $L^p$space
Abstract
We provide a complete description of those Banach algebras that are generated by an invertible isometry of an $L^p$space together with its inverse. Examples include the algebra $PF_p(\mathbb{Z})$ of $p$pseudofunctions on $\mathbb{Z}$, the commutative $C^*$algebra $C(S^1)$ and all of its quotients, as well as uncountably many `exotic' Banach algebras. We associate to each isometry of an $L^p$space, a spectral invariant called `spectral configuration', which contains considerably more information than its spectrum as an operator. It is shown that the spectral configuration describes the isometric isomorphism type of the Banach algebra that the isometry generates together with its inverse. It follows from our analysis that these algebras are semisimple. With the exception of $PF_p(\mathbb{Z})$, they are all closed under continuous functional calculus, and their Gelfand transform is an isomorphism. As an application of our results, we show that Banach algebras that act on $L^1$spaces are not closed under quotients. This answers the case $p=1$ of a question asked by Le Merdy 20 years ago.
 Publication:

arXiv eprints
 Pub Date:
 May 2014
 arXiv:
 arXiv:1405.5589
 Bibcode:
 2014arXiv1405.5589G
 Keywords:

 Mathematics  Functional Analysis;
 Mathematics  Operator Algebras;
 Primary: 46J40;
 46H35;
 Secondary: 47L10
 EPrint:
 36 pages. Changes in v2: the results of Section 2 have been improved and extended, so they were removed to be included elsewhere. We showed that every H\"older exponent not equal to 2 is what we called 'regular', so this notion does not appear anymore. Fixed a number of typos, improved presentation, and added references. Changes in v3: added a new section with an application. Updated references