Restriction of Laplace–Beltrami Eigenfunctions to Arbitrary Sets on Manifolds

Abstract

Abstract Given a compact Riemannian manifold $(M, g)$ without boundary, we estimate the Lebesgue norm of Laplace–Beltrami eigenfunctions when restricted to a wide variety of subsets $\Gamma $ of $M$. The sets $\Gamma $ that we consider are Borel measurable, Lebesguenull but otherwise arbitrary with positive Hausdorff dimension. Our estimates are based on Frostman-type ball growth conditions for measures supported on $\Gamma $. For large Lebesgue exponents $p$, these estimates provide a natural generalization of $L^p$ bounds for eigenfunctions restricted to submanifolds, previously obtained in [ 8, 18, 19, 32]. Under an additional measure-theoretic assumption on $\Gamma $, the estimates are shown to be sharp in this range. As evidence of the genericity of the sharp estimates, we provide a large family of random, Cantor-type sets that are not submanifolds, where the above-mentioned sharp bounds hold almost surely.