Bifurcation of overdetermined capillary problems in a strip domain

Abstract

In this paper, we consider the classical overdetermined capillary problem: \begin{equation*} \begin{cases} \mathrm{div} \left(\frac{\nabla u}{\sqrt{1+|\nabla u|^2}}\right) - bu =0 &~~\mbox{in}~~ Ω, \partial_ν u=κ&~~\mbox{on}~~\partialΩ, u=c &~~\mbox{on}~~\partialΩ, \end{cases} \end{equation*} where $b$, $c$ and $κ$ are positive constants, and $Ω\subset \mathbb{R}^2$. When $Ω$ is an infinite strip, i.e., a domain bounded by two parallel straight lines, there exists a unique one-dimensional solution (called the trivial solution) to this problem. By means of a bifurcation argument, we establish the existence of a critical period $T_*$ at which a branch of non-trivial solutions bifurcates from the trivial one. These solutions are genuinely two-dimensional and are defined in unbounded periodic domains $Ω$ that are diffeomorphic to an infinite strip, yet whose boundaries are no longer straight lines. This result offers a significant physical interpretation in the context of capillary phenomena.