Published online by Cambridge University Press: 14 April 2020
Let $\Omega \subset \mathbb {R}^N$,
$N\geq 2$, be an open bounded connected set. We consider the fractional weighted eigenvalue problem
$(-\Delta )^s u =\lambda \rho u$ in
$\Omega $ with homogeneous Dirichlet boundary condition, where
$(-\Delta )^s$,
$s\in (0,1)$, is the fractional Laplacian operator,
$\lambda \in \mathbb {R}$ and
$ \rho \in L^\infty (\Omega )$.
We study weak* continuity, convexity and Gâteaux differentiability of the map $\rho \mapsto 1/\lambda _1(\rho )$, where
$\lambda _1(\rho )$ is the first positive eigenvalue. Moreover, denoting by
$\mathcal {G}(\rho _0)$ the class of rearrangements of
$\rho _0$, we prove the existence of a minimizer of
$\lambda _1(\rho )$ when
$\rho $ varies on
$\mathcal {G}(\rho _0)$. Finally, we show that, if
$\Omega $ is Steiner symmetric, then every minimizer shares the same symmetry.