Wave Equations with Point Interactions in Finite Energy Space
  Given the abstract wave equation $\ddot\phi-\Delta_\alpha\phi=0$, where $\Delta_\alpha$ is the Laplace operator with a point interaction of strength $\alpha$, we define and study $\bar W_\alpha$, the associated wave generator in the phase space of finite energy states. We prove the existence of the phase flow generated by $\bar W_\alpha$, and describe its most relevant properties with particular emphasis on the associated symplectic structure and scattering theory 
Massimo Bertini, Diego Noja, Andrea Posilicano