Parabolic--Elliptic Dynamics with Local--Nonlocal Coupled Operators

In this paper, we study two local--nonlocal settings for parabolic--elliptic evolution systems. In our problems we have a disjoint partition of the spacial domain $\Omega$ as $\Omega=A\cup B$ and we first consider a local parabolic equation posed in $A$ with a nonlocal elliptic balance equation acting in the complementary subdomain $B$. Next, we reverse the roles and take a local elliptic equation posed in $A$ coupled with a nonlocal parabolic equation acting in $B$. In both models, the interaction between the two regions is driven by a nonlocal transmission term given by a kernel that transfers mass across the interface, giving rise to a mixed local--nonlocal, elliptic--parabolic dynamics. We consider Neumann boundary conditions for both problems. To being our analysis we first establish the existence and uniqueness of solutions using a fixed point argument. Then, we provide a detailed analysis of their qualitative behavior. In particular, we show that the coupling structure induces a natural energy functional whose gradient flow governs the evolution, despite the elliptic--parabolic nature of the system. As it is expected in Neumann settings, we prove that the total mass in the whole domain $\Omega$ is preserved in time. We also analyze the long-time behaviour and obtain decay estimates for the parabolic component, which in turn drive the convergence of the elliptic part to a constant solution. Finally, we prove that the parabolic--elliptic problem under consideration is the limit of a purely parabolic problem when a parameter that controls the speed of the dynamic at which one component evolves goes to zero.