Nonlocal free boundary minimal surfaces

We introduce the nonlocal analogue of the classical free boundary minimal hypersurfaces in an open domain $\Omega$ of $\mathbb{R}^n$ as the (boundaries of) critical points of the fractional perimeter $\operatorname{Per}_s(\cdot,\,\Omega )$ with respect to inner variations leaving $\Omega$ invariant. We deduce the Euler-Lagrange equations and prove a few surprising features, such as the existence of critical points without boundary and a strong volume constraint in $\Omega$ for unbounded hypersurfaces. Moreover, we investigate stickiness properties and regularity across the boundary.