Symmetry, uniqueness and nondegeneracy of positive solutions of the Choquard equation

Abstract

We study positive solutions \(Q\in H^1(\mathbb R^N)\) of \[-ΔQ+Q=(I_α*Q^p)Q^{p-1},\] where \(I_α\) is the Riesz potential of order \(α\), \(N\ge1\), \(0<α<N\), \(p>1+α/N\), and \((N-2)p<N+α\). We prove that every such solution is radially symmetric and strictly decreasing about some point. For \(p\ge2\), we establish uniqueness up to translations and show that the real linearized operator has Morse index one and kernel spanned by \(\partial_1Q,\ldots,\partial_NQ\). The symmetry proof uses the method of moving planes. Uniqueness follows from nondegeneracy and compactness through a continuation argument.