Castrillón López, MarcoGotay, Mark J.Marsden, Jerrold E.Krupkova, OlgaSaunders , David2023-06-202023-06-202009978-1-60456-920-9https://hdl.handle.net/20.500.14352/53257We show how to \concatenate" variational principles over different bases into one over a single base, thereby providing a unifed Lagrangian treatment of interacting systems. As an example we study a Klein Gordon feld interacting with a mesically charged particle. We employ our method to give a novel group-theoretic derivation of the kinetic stress-energy-momentum tensor density corresponding to the particle.engbook partopen access515.16Geometria algebraica1201.01 Geometría Algebraica