Differences between Robin and Neumann eigenvalues

Zeev Rudnick, Igor Wigman, Nadav Yesha

Let $\Omega \subset {\mathbb{R}}^2$ be a bounded planar domain, with piecewise smooth boundary $\partial \Omega$. For $\sigma >0$, we consider the Robin boundary value problem \[ -Δf =λf, \qquad \frac…