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

In this paper, we prove that the Brezis-Nirenberg problem 12 06u=|u|^{p 121}u+\u3b5u in \u3a9, u=0 on 02\u3a9, where \u3a9 is a symmetric bounded smooth domain in R^N , N 65 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 \u3b5 > 0 sufficiently small