Variational inequalities for the spectral fractional Laplacian
  In this paper we study the obstacle problems for the Navier (spectral) fractional Laplacian $\left(-\Delta_\Omega\right)^{\!s}$ of order $s\in(0,1)$, in a bounded domain $\Omega\subset\mathbb R^n$. 
Roberta Musina and Alexander I. Nazarov
math.AP