Representation of quasi-periodic functions and Hausdorff-Young inequalities for Besicovitch almost periodic functions

TL;DR

This paper characterizes quasi-periodic functions on tori, establishes ergodic properties, and proves Hausdorff-Young inequalities for Besicovitch almost periodic functions, linking spectral properties with function regularity.

Contribution

It introduces a novel isomorphism between quasi-periodic and periodic function algebras, simplifying proofs of key inequalities and analyzing regularity of generating functions.

Findings

Characterization of unique ergodicity for certain $bR^d$-actions.

Establishment of a Weyl-type theorem for these actions.

Simplified proof of Hausdorff-Young inequalities for Besicovitch almost periodic functions.

Abstract

For a class of $\mathbb{R}^d$-ations and $\mathbb{Z}^d$-actions on the $n$-dimensional torus $\mathbb{T}^n$, we characterize their unique ergodicity and establish a theorem of Weyl type. This result allows us to establish an isomorphism between the Banach algebra of quasi-periodic functions with spectrum in a given $\mathbb{Z}$-module and the Banach algebra of periodic functions on a torus. This, in return, allows us to give a very simple proof of Hausdorff-Young inequalities for Besicovitch almost periodic functions. The regularity of the parent function of a quasi-periodic function is also studied.