On the Absolutely Continuous Spectrum of Sturm-Liouville Operators with Applications to Radial Quantum Trees

We consider standard subordinacy theory for general Sturm–Liouville operators and give criteria when boundedness of solutions implies that no subordinate solutions exist. As applications, we prove a Weidmann-type result for general Sturm–Liouville operators and investigate the absolutely continuous spectrum of radially symmetric quantum trees.