A characterization of algebraic measures
The aim of this paper is to show that, in various situations, the only continuous linear (or not) map that transforms a convolution product into a pointwise product is a Fourier transform. We focus on the cyclic groups ℤ/nℤ, the integers ℤ, the torus 𝕋 and the real line. We also ask a related question for the twisted convolution.
For a locally compact, abelian group , we study the space of functions on belonging locally to the Fourier algebra and with -behavior at infinity. We give an abstract characterization of the family of spaces abelian by its hereditary properties.
Suppose that is a locally compact abelian group with a Haar measure . The -ball of a continuous translation invariant pseudo-metric is called -dimensional if for all . We show that if is a compact symmetric neighborhood of the identity with for all , then is contained in an -dimensional ball, , of positive radius in some continuous translation invariant pseudo-metric and .
Let be a Fourier-Stieltjes transform, defined on the discrete real line and such that the corresponding measure on the dual group vanishes on the set of characters, continuous on . Then for every , has a vanishing interior Lebesgue measure. If the statement is not generally true. The result is applied to prove a theorem of Rosenthal.
We give an elementary proof for the case of the circle group of the theorem of O. Hatori and E. Sato, which states that every measure on a compact abelian group G can be decomposed into a sum of two measures with a natural spectrum and a discrete measure.