A family of special case of sequential warped product manifolds with semi-Riemannian Einstein metrics

We derive the general formulas for a special configuration of the sequential warped product semi-Riemannian manifold to be Einstein, where the base-manifold is the product of two manifolds both equipped with a conformal metrics. Subsequently we study the case in which these two manifolds are conformal to a $n_1$-dimensional and $n_2$-dimensional pseudo-Euclidean space, respectively. For the latter case, we prove the existence of a family of solutions that are invariant under the action of a $(n_1-1)$-dimensional group of transformations to the case of positive constant Ricci curvature ($\lambda>0$).
Comment: Latest version has minor changes and added references. Accepted for publication in: Journal of Geometric Mechanics (AIMS - America Institute of Mathematical Sciences)