Uniqueness of least energy solutions to the fractional Lane-Emden equation in the ball

We prove uniqueness of least-energy solutions to the fractional Lane-Emden equation, under homogeneous Dirichlet exterior conditions, when the underlying domain is a ball $B\subset {\mathbb{R}}^N$. The equation is characterized by a superlinear, subcritical power-like nonlinearity. The proof makes use of Morse theory and is inspired by some results obtained by C. S. Lin in the '90s. A new Hopf’s Lemma-type result shown in this paper is an essential element in the proof of nondegeneracy of least-energy solutions.