Bifurcation domains from any high eigenvalue for an overdetermined elliptic problem

TL;DR

This paper constructs new unbounded domains with specific bifurcation properties for high eigenvalues in an overdetermined elliptic problem, providing the first such examples for eigenvalues with index $k \\geq 3$, and challenges existing conjectures.

Contribution

It introduces the first construction of unbounded domains bifurcating from the straight cylinder for all eigenvalues with index $k \\geq 3$, expanding understanding of overdetermined eigenvalue problems.

Findings

Constructed $k$ smooth unbounded domains for $k \\geq 3$

Domains admit non-symmetric solutions with sign changes

Counterexamples to the Berenstein conjecture

Abstract

In this paper, we consider the following overdetermined eigenvalue problem on an unbounded domain $\Omega\subset\mathbb{R}^{N+1}$ with $N\geq1$ \begin{equation} \left\{ \begin{array}{ll} -\Delta u=\lambda u\,\, &\text{in}\,\, \Omega,\\ u=0 &\text{on}\,\, \partial \Omega,\\ \partial_\nu u=\text{const} &\text{on}\,\, \partial \Omega. \end{array} \right.\nonumber \end{equation} Let $\lambda_k$ be the $k$-th eigenvalue of the zero-Dirichlet Laplacian on the unit ball for any $k\in \mathbb{N^+}$ with $k\geq 3$. We can construct $k$ smooth families of nontrivial unbounded domains $\Omega$, bifurcating from the straight cylinder, which admit a nonsymmetric solution with changing the sign by $k-1$ times to the overdetermined problem. While the existence of such domains for $k=1,2$ has been well-known, to the best of our knowledge this is the first construction for any positive integer $k\geq 3$. Due to the complexity of studying high eigenvalue problem, our proof involves some novel analytic ingredients. These results can be regarded as counterexamples to the Berenstein conjecture on unbounded domain.