Vector valued piecewise continuous almost automorphic functions and some consequences

TL;DR

This paper extends the concept of piecewise continuous almost automorphic functions to Banach space-valued functions, explores their properties, and applies them to differential equations and heat equations, providing new characterizations and solutions.

Contribution

It introduces a new class of Banach space-valued piecewise continuous almost automorphic functions and studies their algebraic and functional properties, with applications to differential equations.

Findings

The class forms a Banach algebra if the space is a Banach algebra.

Provides a new characterization of compact almost automorphic functions.

Shows almost automorphic solutions of differential equations are compact almost automorphic.

Abstract

In the present work, for $\mathbb{X}$ a Banach space, the notion of piecewise continuous $\mathbb{Z}$-almost automorphic functions with values in finite dimensional spaces is extended to piecewise continuous $\mathbb{Z}$-almost automorphic functions with values in $\mathbb{X}$. Several properties of this class of functions are provided, in particular it is shown that if $\mathbb{X}$ is a Banach algebra, then this class of functions constitute also a Banach algebra; furthermore, using the theory of $\mathbb{Z}$-almost automorphic functions, a new characterization of compact almost automorphic functions is given. As consequences, with the help of $\mathbb{Z}$-almost automorphic functions, it is presented a simple proof of the characterization of almost automorphic sequences by compact almost automorphic functions; the method permits us to give explicit examples of compact almost automorphic functions which are not almost periodic. Also, using the theory developed here, it is shown that almost automorphic solutions of differential equations with piecewise constant argument are in fact compact almost automorphic. Finally, it is proved that the classical solution of the $1D$ heat equation with continuous $\mathbb{Z}$-almost automorphic source is also continuous $\mathbb{Z}$-almost automorphic; furthermore, we comment applications to the existence and uniqueness of the asymptotically continuous $\mathbb{Z}$-almost automorphic mild solution to abstract integro-differential equations with nonlocal initial conditions.