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Non-symmetric solutions to an overdetermined problem for the Helmholtz equation in the plane

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arxiv 2509.00455 v1 pith:7ZTEDB7E submitted 2025-08-30 math.AP

Non-symmetric solutions to an overdetermined problem for the Helmholtz equation in the plane

classification math.AP
keywords omegapartialqquadtextalignedatlambdanewlineoverdetermined
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In this note we construct smooth bounded domains $\Omega \subset \mathbb R^2$, other than disks, for which the overdetermined problem $$ \left\{ \begin{alignedat}{2} \Delta u + \lambda u &= 0 &\qquad& \text{ in } \Omega, \newline u &= b &\qquad& \text{ on } \partial \Omega, \newline \frac{\partial u}{\partial n} &= c &\qquad& \text{ on } \partial \Omega \end{alignedat} \right. $$ has a solution for some constants $\lambda,b,c \ne 0$. These appear to be the first counterexamples to a conjecture of Willms and Gladwell [WG94].

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Cited by 3 Pith papers

Reviewed papers in the Pith corpus that reference this work. Sorted by Pith novelty score.

  1. A computer-assisted counterexample to the planar Pompeiu and Schiffer conjectures

    math.AP 2026-08 accept novelty 9.0

    A computer-assisted proof constructs a bounded simply connected non-circular planar domain with a nonconstant Neumann eigenfunction equal to 1 on the boundary, disproving Schiffer's and Pompeiu's conjectures.

  2. On two-dimensional steady compactly supported Euler flows with constant vorticity

    math.AP 2026-02 accept novelty 7.0

    Existence, rigidity, and stability theorems are established for compactly supported steady Euler flows with constant vorticity in partially, two-phase, and fully overdetermined free-boundary problems.

  3. On two-dimensional steady compactly supported Euler flows with constant vorticity

    math.AP 2026-02 conditional novelty 6.0

    Annular equilibria of constant-vorticity Euler flows bifurcate into non-annular admissible domains at specific vorticity values, with rigidity and Neumann-stability results for three classes of free-boundary problems.