The role of the boundary in the existence of blow-up solutions for a doubly critical elliptic problem

In this paper we consider a doubly critical nonlinear elliptic problem with Neumann boundary conditions. The existence of blow-up solutions for this problem is related to the blow-up analysis of the classical geometric problem of prescribing negative scalar curvature $K=-1$ on a domain of ${\mathbb{R}}^n$ and mean curvature $H=D(n(n-1){)}^{-1\mathrm{/}2}$, for some constant $D>1$, on its boundary, via a conformal change of the metric. Assuming that $n\ge 6$ and $D>\sqrt{(n+1)\mathrm{/}(n-1)}$, we establish the existence of a positive solution which concentrates around an elliptic boundary point which is a nondegenerate critical point of the original mean curvature.