On the High Energy Behavior of Nonlinear Functionals of Random Eigenfunctions on ${\mathbb{S}}^d$

In this short survey we recollect some of the recent results on the high energy behavior (i.e., for diverging sequences of eigenvalues) of nonlinear functionals of Gaussian eigenfunctions on the $d$-dimensional sphere $\mathbb S^d$,$d\ge 2$. We present a quantitative Central Limit Theorem for a class of functionals whose Hermite rank is two, which includes in particular the empirical measure of excursion sets in the non-nodal case. Concerning the nodal case, we recall a CLT result for the defect on ${\mathbb{S}}^2$. The key tools are both, the asymptotic analysis of moments of all order for Gegenbauer polynomials, and so-called Fourth-Moment theorems.