Problems related to the concentration of eigenfunctions

We survey recent results related to the concentration of eigenfunctions. We also prove some new results concerning ball-concentration, as well as showing that eigenfunctions saturating lower bounds for $L^1$-norms must also, in a measure theoretical sense, have extreme concentration near a geodesic.Comment: 13 page

Concerning Nikodym-type sets in 3-dimensional curved spaces

We obtain estimates for maximal functions that arise when one studies Nikodym-type sets. We also formulate a curvature condition that allows favorable estimates for these maximal functions

Semiclassical limits of eigenfunctions on flat nn-dimensional tori

We provide a proof of the conjecture formulated in \cite{Jak97,JNT01} which states that on a $n$-dimensional flat torus \T^{n}, the Fourier transform of squares of the eigenfunctions $|\phi_\lambda|^2$ of the Laplacian have uniform $l^n$ bounds that do not depend on the eigenvalue $\lambda$. The proof is a generalization of the argument by Jakobson, {\it et al}. for the lower dimensional cases. These results imply uniform bounds for semiclassical limits on \TT^{n+2}. We also prove a geometric lemma that bounds the number of codimension-one simplices which satisfy a certain restriction on an $n$-dimensional sphere $S^n(\lambda)$ of radius $\sqrt{\lambda}$ and use it in the proof.Comment: 10 pages; Canadian Mathematical Bulletin, 201