Quasi-linear criticality theory and Green’s functions on graphs
摘要
We study energy functionals associated with quasi-linear Schrödinger operators on infinite graphs, and develop characterisations of criticality via Green’s functions, harmonic functions of minimal growth and capacities. We prove a quasi-linear version of the Agmon–Allegretto–Piepenbrink theorem, which says that the energy functional is non-negative if and only if there is a positive superharmonic function. Furthermore, we show that a positive minimal Green’s function exists if and only if the energy functional is subcritical. Comparison principles and maximum principles are the main tools in the proofs.