Equations of Motion from Field Equations and a Gauge-invariant Variational Principle for the Motion of Charged Particles

摘要

New, gauge-independent, second-order Lagrangian for the motion of classical,charged test particles is proposed. It differs from the standard,gauge-dependent, first order Lagrangian by boundary terms only. A new method ofderiving equations of motion from field equations is developed. When applied toclassical electrodynamics, this method enables us to obtain unambigously theabove, second order Lagrangian from the general energy-momentum conservationprinciple.