On the classification of Serrin planar domains

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Hauptverfasser: Cerezo, Alberto, Fernandez, Isabel, Mira, Pablo
Format: Preprint
Veröffentlicht: 2026
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author Cerezo, Alberto
Fernandez, Isabel
Mira, Pablo
author_facet Cerezo, Alberto
Fernandez, Isabel
Mira, Pablo
contents We show that all smooth ring domains $Ω\subset \mathbb{R}^2$ that admit a solution to Serrin's classical problem $Δu+2=0$ with locally constant overdetermined boundary conditions along $\partial Ω$ can be described as algebro-geometric potentials of the mKdV hierarchy. The same result holds for periodic unbounded domains with two boundary components. In particular, any such domain is determined by suitable holomorphic data in some algebraic curve. As a consequence, the space of all Serrin ring domains, or periodic Serrin bands, can be ordered into a sequence of finite-dimensional complexity levels. By studying the first non-trivial level, given by elliptic functions, we construct: $(i)$ a global $1$-parameter family of periodic solutions to Serrin's problem that interpolates between a flat band and a chain of disks along an axis, following an unduloid pattern, and $(ii)$ for any $n>1$, a two-dimensional moduli space ${\bf T}_n$ of non-radial Serrin ring domains with a dihedral symmetry group of order $2n$. This moduli space ${\bf T}_n$ is geometrically a triangle, and has radial bands on one side of ${\bf T}_n$, and a necklace of $n$ pairwise tangent disks distributed along the unit circle at its opposite vertex in ${\bf T}_n$.
format Preprint
id arxiv_https___arxiv_org_abs_2601_09649
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle On the classification of Serrin planar domains
Cerezo, Alberto
Fernandez, Isabel
Mira, Pablo
Analysis of PDEs
Differential Geometry
35N25, 35B32, 53A10
We show that all smooth ring domains $Ω\subset \mathbb{R}^2$ that admit a solution to Serrin's classical problem $Δu+2=0$ with locally constant overdetermined boundary conditions along $\partial Ω$ can be described as algebro-geometric potentials of the mKdV hierarchy. The same result holds for periodic unbounded domains with two boundary components. In particular, any such domain is determined by suitable holomorphic data in some algebraic curve. As a consequence, the space of all Serrin ring domains, or periodic Serrin bands, can be ordered into a sequence of finite-dimensional complexity levels. By studying the first non-trivial level, given by elliptic functions, we construct: $(i)$ a global $1$-parameter family of periodic solutions to Serrin's problem that interpolates between a flat band and a chain of disks along an axis, following an unduloid pattern, and $(ii)$ for any $n>1$, a two-dimensional moduli space ${\bf T}_n$ of non-radial Serrin ring domains with a dihedral symmetry group of order $2n$. This moduli space ${\bf T}_n$ is geometrically a triangle, and has radial bands on one side of ${\bf T}_n$, and a necklace of $n$ pairwise tangent disks distributed along the unit circle at its opposite vertex in ${\bf T}_n$.
title On the classification of Serrin planar domains
topic Analysis of PDEs
Differential Geometry
35N25, 35B32, 53A10
url https://arxiv.org/abs/2601.09649