Copyright © 2006 Hindawi Publishing Corporation. All rights reserved.
Concentration estimates for Emden-Fowler equations with boundary singularities and critical growth
Department of Mathematics, University of British Columbia Vancouver, BC Canada V6T 1Z2 E-mail address: nassif{at}math.ubc.ca
Laboratoire J.A. Dieudonné, Université de Nice Sophia-Antipolis Parc Valrose, 06108 Nice Cedex 2, France E-mail address: frobert{at}math.unice.fr
We establish—among other things—existence and multiplicity of solutions for the Dirichlet problem 
i
iiu + |u|2*–2u/|x|s = 0 on a smooth bounded domain 
of 
n(n 
3) involving the critical Hardy-Sobolev exponent 2* = 2(n – s)/(n – 2), where 0 < s < 2, and in the case where zero (the point of singularity) is on the boundary . Just as in the Yamabe-type nonsingular framework (i.e., when s = 0), there is no nontrivial solution under global convexity assumption (e.g., when is star-shaped around 0). However, in contrast to the nonsatisfactory situation of the nonsingular case, we show the existence of an infinite number of solutions under an assumption of local strict concavity of at 0 in at least one direction. More precisely, we need the principal curvatures of at 0 to be nonpositive but not all vanishing. We also show that the best constant in the Hardy-Sobolev inequality is attained as long as the mean curvature of at 0 is negative, extending the results of Ghoussoub and Kang in 2004 and completing our result in 2005 to include dimension 3. The key ingredients in our proof are refined concentration estimates which yield compactness for certain Palais-Smale sequences which do not hold in the nonsingular case.