On the global well-posedness and self-similar solutions for a nonlinear elliptic problem with a dynamic boundary condition

We are concerned with a semilinear elliptic equation in the half-space, subject to a nonlinear dynamic boundary condition. We establish the global well-posedness of solutions in a new setting for the problem, namely the framework of Morrey spaces. These are strictly larger than $L^p$ and weak-$L^p$ spaces, accommodating a broader class of rough initial data, including homogeneous and nondecaying (at infinity) profiles. In our analysis, we consider functional spaces invariant under the natural scaling of the problem, which enables the construction of self-similar solutions. To achieve this, we need to derive key estimates in Morrey spaces for certain interior and boundary operators that arise from the corresponding integral formulation. Furthermore, we obtain some qualitative properties of the solutions, such as positivity, symmetry, and asymptotic stability. Leveraging this last property, we show the existence of self-similar attractor basins and construct a class of solutions that are asymptotically self-similar.