Lower bounds for eigenfunction restrictions in lacunary regions

Abstract: Let $(M,g)$ be a compact, smooth Riemannian manifold and ${u_h}$ be a sequence of $L^2$-normalized Laplace eigenfunctions that has a localized defect measure $\mu$ in the sense that $ M \setminus \text{supp}(\pi_* \mu) \neq \emptyset$ where $\pi:T^*M \to M$ is the canonical projection. Using Carleman estimates we prove that for any real-smooth closed hypersurface $H \subset (M\setminus \text{supp} (\pi_* \mu))$ sufficiently close to $ \text{supp}(\pi_* \mu),$ and for all $\delta >0,$ $$ \int_{H} |u_h|^2 d\sigma \geq C_{\delta}\, e^{- [\, d(H, \text{supp}(\pi_* \mu)) + \,\delta] /h} $$ as $h \to 0^+$. We also show that the result holds for eigenfunctions of Schr\"odinger operators and give applications to eigenfunctions on warped products and joint eigenfunctions of quantum completely integrable (QCI) systems.