On a sharp lemma of Cassels and Montgomery on manifolds

Luca Brandolini, Bianca Gariboldi, Giacomo Gigante

Let $\left(\mathcal{M},g\right)$ be a $d$-dimensional compact connected Riemannian manifold and let ${\left\{{\phi }_m\right\}}_{m=0}^{+\infty }$ be a complete sequence of orthonormal…