Hardy-singular boundary mass and Sobolev-critical variational problems

Ghoussoub, Nassif; Robert, Frédéric

doi:10.2140/apde.2017.10.1017

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Hardy-singular boundary mass and Sobolev-critical variational problems

Nassif Ghoussoub and Frédéric Robert

Vol. 10 (2017), No. 5, 1017–1079

DOI: 10.2140/apde.2017.10.1017

Abstract

We investigate the Hardy–Schrödinger operator $L_{γ} = - Δ - γ ∕ | x |^{2}$ on smooth domains $Ω \subset ℝ^{n}$ whose boundaries contain the singularity $0$ . We prove a Hopf-type result and optimal regularity for variational solutions of corresponding linear and nonlinear Dirichlet boundary value problems, including the equation $L_{_{γ}} u = u^{2^{⋆} (s) - 1} ∕ | x |^{s}$ , where $γ < \frac{1}{4} n^{2}$ , $s \in [0, 2)$ and $2^{⋆} (s) : = 2 (n - s) ∕ (n - 2)$ is the critical Hardy–Sobolev exponent. We also give a complete description of the profile of all positive solutions — variational or not — of the corresponding linear equation on the punctured domain. The value $γ = \frac{1}{4} (n^{2} - 1)$ turns out to be a critical threshold for the operator $L_{γ}$ . When $\frac{1}{4} (n^{2} - 1) < γ < \frac{1}{4} n^{2}$ , a notion of Hardy singular boundary mass $m_{γ} (Ω)$ associated to the operator $L_{γ}$ can be assigned to any conformally bounded domain $Ω$ such that $0 \in \partial Ω$ . As a byproduct, we give a complete answer to problems of existence of extremals for Hardy–Sobolev inequalities, and consequently for those of Caffarelli, Kohn and Nirenberg. These results extend previous contributions by the authors in the case $γ = 0$ , and by Chern and Lin for the case $γ < \frac{1}{4} {(n - 2)}^{2}$ . More specifically, we show that extremals exist when $0 \leq γ \leq \frac{1}{4} (n^{2} - 1)$ if the mean curvature of $\partial Ω$ at $0$ is negative. On the other hand, if $\frac{1}{4} (n^{2} - 1) < γ < \frac{1}{4} n^{2}$ , extremals then exist whenever the Hardy singular boundary mass $m_{γ} (Ω)$ of the domain is positive.

Keywords

Hardy–Schrödinger operator, Hardy-singular boundary mass, Hardy–Sobolev inequalities, mean curvature

Mathematical Subject Classification 2010

Primary: 35J35, 35J60, 58J05, 35B44

Milestones

Received: 4 January 2016

Revised: 23 February 2017

Accepted: 3 April 2017

Published: 1 July 2017

Authors

Nassif Ghoussoub
Department of Mathematics 1984 Mathematics Road University of British Columbia Vancouver, BC V6T 1Z2 Canada

Frédéric Robert
Institut Élie Cartan Université de Lorraine BP 70239 F-54506 Vandœuvre-lès-Nancy France

Vol. 10, No. 5, 2017