Harmonic balls and two-phase Schwarz function

TL;DR

This paper introduces harmonic balls in sub-domains of Euclidean space and extends the Schwarz function concept to a two-phase version, providing foundational properties and encouraging further research in these areas.

Contribution

It defines harmonic balls and two-phase Schwarz functions, extending classical concepts and establishing basic properties to stimulate further investigation.

Findings

Harmonic balls are introduced with a mean value property for harmonic functions.

Two-phase Schwarz functions are generalized for complex analytic functions.

The paper provides initial properties and insights to motivate future research.

Abstract

Here we shall introduce the concept of harmonic balls/spheres in sub-domains of $\R^n$, through a mean value property for a sub-class of harmonic functions on such domains. In the complex plane, and for analytic functions, a similar concept fails to exist due to the fact that analytic functions can not have prescribed data on the boundary. Nevertheless, a two-phase version of the problem does exists, and gives rise to the generalization of the well-known Schwarz function to the case of two-phase Schwarz function. Our primary goal is to derive simple properties for these problems, and tease the appetites of experts working on Schwarz function and related topics. Hopefully these two concepts will provoke further study of the topic.