Small-scale mass estimates for Neumann eigenfunctions: piecewise smooth planar domains

Abstract: Let $\Omega$ be a piecewise-smooth, bounded convex domain in $\R^2$ and consider $L^2$-normalized Neumann eigenfunctions $\phi_{\lambda}$ with eigenvalue $\lambda^2$. Our main result is a small-scale {\em non-concentration} estimate: We prove that for {\em any} $x_0 \in \overline{\Omega},$ (including boundary and corner points) and any $\delta \in [0,1),$ $$ | \phi_\lambda |_{B(x_0,\lambda^{-\delta})\cap \Omega} = O(\lambda^{-\delta/2}).$$ The proof is a stationary vector field argument combined with a small scale induction argument.