© 1990 by London Mathematical Society
Spectral Extension for Measures
Département de Mathématiques et Informatique, CSP, Université Paris-Nord Avenue J.-B. Clément, 93430 Villetaneuse, France
The main difficulty when working on spectral properties of measures on a locally compact abelian group lies in the fact that the algebra M(G) has a very large and intricate Gelfand spectrum, even when the group G is T or R. Besides, every measure or finite collection of measures in M{G) is contained in a small subalgebra isomorphic to some space Ll(µ), and the characters (multiplicative linear functionals) of such a subalgebra are the solutions of a simple functional equation in L
(µ). The natural question is which of these characters can be extended to M{G). We give an explicit criterion based on a point property and a more theoretical condition which shows that spectral properties of measures can be determined inside such small subalgebras.