ELECTROMAGNETIC DEFLECTION OF SPINNING PARTICLES

We show that it is possible to obtain self-consistent and physically acceptable relativistic classical equations of motion for a pointlike spin-half particle possessing an electric charge and a magnetic dipole moment, directly from a manifestly covariant Lagrangian, if the classical degrees of freedom are appropriately chosen. It is shown that the equations obtained encompass the well-tested Lorentz force and Thomas-Bargmann-Michel-Telegdi spin equations, as well as providing a definite specification of the classical magnetic dipole force, whose exact form has been the subject of recent debate. Radiation reaction — the force and torque on an accelerated particle due to its self-interaction — is neglected at this stage.