A Gauge-invariant Hamiltonian Description of the Motion of Charged Test Particles

New, gauge-independent, second-order Lagrangian for the motion of classical, charged test particles is used to derive the corresponding Hamiltonian formulation. For this purpose a Hamiltonian description of the theories derived from the second-order Lagrangian is presented. Unlike in the standard approach, the canonical momenta arising here are explicitely gauge-invariant and have a clear physical intepretation. The reduced symplectic form is equaivalent to the Souriau's form. This approach illustrates a new method of deriving equations of motion from field equations.Comment: LATEX, 15 page

Generation of a dipole moment by external field in Born-Infeld non-linear electrodynamics

The mechanism for the generation of a dipole moment due to an external field is presented for the Born-Infeld charged particle. The 'polarizability coefficient' is calculated: it is proportional to the third power of the characteristic length in the Born-Infeld theory. Some physical implications are briefly discussed.Comment: 8 pages, LATE