Let \(X\) be a Riemannian symmetric space of noncompact type. Mathematically, the resonances appear as poles of the meromorphic continuation of the resolvent of the Laplacian of \(X\). The basic problems are the existence, location, counting estimates and geometric interpretation of the resonances. All these problems are nowadays understood when \(X\) is a real rank one space. In the paper under review, the authors study the case when \(X=G/K\) is a Riemannian symmetric space of real rank two and restricted root system \(BC_2\) or \(C_2\) (except for \(G=SO_0(p,2)\) with \(p>2\) odd). For all such spaces the analysis of the meromorphic continuation of the resolvent of the Laplacian can be deduced from some problem on a direct product \(X_1\times X_1\) of a Riemannian symmetric space of rank not isomorphic to the real hyperbolic space.
For the entire collection see [Zbl 1354.53006].