Sign-changing tower of bubbles for the Brezis-Nirenberg problem

In this paper, we prove that the Brezis-Nirenberg problem −∆u=|u|^{p−1}u+εu in Ω, u=0 on ∂Ω, where Ω is a symmetric bounded smooth domain in R^N , N ≥ 7 and p = {N+2}/{N-2} , has a solution with the shape of a tower of two bubbles with alternate signs, centered at the center of symmetry of the domain, for all ε > 0 sufficiently small.