Cascade of minimizers for a nonlocal isoperimetric problem in thin domains

For $Ω_\e=(0,\e)\times (0,1)$ a thin rectangle, we consider minimization of the two-dimensional nonlocal isoperimetric problem given by \[ \inf_u E^γ_{Ω_\e}(u)\] where \[ E^γ_{Ω_\e}(u):= P_{Ω_\e}(\{u(x)=1\})+γ\int_{Ω_\e}\abs{\nabla{v}}^2\,dx \] and the minimization is taken over competitors $u\in BV(Ω_\e;\{\pm 1\})$ satisfying a mass constraint $\fint_{Ω_\e}u=m$ for some $m\in (-1,1)$. Here $P_{Ω_\e}(\{u(x)=1\})$ denotes the perimeter of the set $\{u(x)=1\}$ in $Ω_\e$, $\fint$ denotes the integral average and $v$ denotes the solution to the Poisson problem \[ -Δv=u-m\;\mbox{in}\;Ω_\e,\quad\nabla v\cdot n_{\partialΩ_\e}=0\;\mbox{on}\;\partialΩ_\e,\quad\int_{Ω_\e}v=0.\] We show that a striped pattern is the minimizer for $\e\ll 1$ with the number of stripes growing like $γ^{1/3}$ as $γ\to\infty.$ We then present generalizations of this result to higher dimensions.

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