On the surface average for harmonic functions: a stability inequality

Autor: Giovanni Cupini, Ermanno Lanconelli
Jazyk: English<br />Italian
Rok vydání: 2024
Předmět:
Zdroj: Bruno Pini Mathematical Analysis Seminar, Vol 14, Iss 2, Pp 129-138 (2024)
Druh dokumentu: article
ISSN: 2240-2829
DOI: 10.6092/issn.2240-2829/18860
Popis: In this article we present some of the main aspects and the most recent results related to the following question: If the surface mean integral of every harmonic function on the boundary of an open set D is "almost'' equal to the value of these functions at x0 in D, then is D "almost'' a ball with center x0? This is the stability counterpart of the rigidity question (the statement above, without the two "almost'') for which several positive answers are known in literature. A positive answer to the stability problem has been given in a paper by Preiss and Toro, by assuming a condition that turns out to be sufficient for ∂D to be geometrically close to a sphere. This condition, however, is not necessary, even for small Lipschitz perturbations of smooth domains, as shown in our recent paper, in which a stability inequality is obtained by assuming only a local regularity property of the boundary of D in at least one of its points closest to x0.
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