Not yet reviewed by Pith; the record is open.

Our aim in this paper is to study local rigidity for metrics defined on a compact manifold $M$ with boundary satisfying constant scalar curvature on $M$ and constant mean curvature on $\partial M$. We present some geometrical hypotheses ensuring local rigidity for both, the general Riemannian and the warped metric case. These conditions arise from the study of a spectral problem which is not included within the classical problems (Neumann, Steklov,...) that we call "mixed eigenvalue problem". Finally, we apply our previous results for the spatial slice of the de Sitter and Anti-de Sitter Schwarzschild spacetimes.