A nonlinear Klein-Gordon equation on a star graph

Abstract: We study local well-posedness and orbital stability/instability of standing waves for a first order system associated with a nonlinear Klein-Gordon equation on a star graph. The proof of the well-posedness uses a classical fixed point argument and the Hille-Yosida theorem. Stability study relies on the linearization approach and recent results for the NLS equation with the $\delta$-interaction on a star graph.