Polygons and multi-product of eigenfunctions

Emmett L. Wyman, Yakun Xi, Yi Zhang

Let $M$ be a compact Riemannian manifold without boundary, with $L^2$-normalized Laplace-Beltrami eigenfunctions $\{e_j{\}}_j$, which satisfy $\hat{I}{”}_g{e}_j=-\hat{I}{»}_j^2{e}_j$. We study the f…