Stability of square root domains associated with elliptic systems of PDEs on nonsmooth domains

Abstract: We discuss stability of square root domains for uniformly elliptic partial differential operators $L_{a,\Omega,\Gamma} = -\nabla\cdot a \nabla$ in $L^2(\Omega)$, with mixed boundary conditions on $\partial \Omega$, with respect to additive perturbations. We consider open, bounded, and connected sets $\Omega \in \mathbb{R}^n$, $n \in \mathbb{N} \backslash{1}$, that satisfy the interior corkscrew condition and prove stability of square root domains of the operator $L_{a,\Omega,\Gamma}$ with respect to additive potential perturbations $V \in L^p(\Omega) + L^{\infty}(\Omega)$, $p>n/2$. Special emphasis is put on the case of uniformly elliptic systems with mixed boundary conditions.