Abstract
In this paper, we considered the Neumann elliptic equation (P-e): -?u + K(x)u = u((n+2)/(n-2)-e), u > 0 in O, ?u/?? = 0 on ?O, where O is a smooth bounded domain in R-n, n = 6, e is a small positive real and K is a smooth positive function on (O). Using refined asymptotic estimates of the gradient of the associated Euler-Lagrange functional, we constructed simple and non-simple interior bubbling solutions of (P-e) which allowed us to prove multiplicity results for (P-e) provided that e is small. The existence of non-simple interior bubbling solutions is a new phenomenon for the positive solutions of subcritical problems.