RELATIVISTIC DYNAMICS OF WAVE-PACKETS FOR SPIN-1 2 PARTICLES IN AN ELECTROMAGNETIC-FIELD/

Classical and quantum dynamics of wave packets for spin-1/2 particles are analysed in the presence of an electromagnetic field. An almost ex act agreement is found between these two approaches, both in the stron g and the weak coupling limits. The question of negative energy states is discussed, and it is shown that they are not produced in such an i nteraction. The divergence problem of the perturbation expansion of th e particles wavefunction is discussed, the source of which is explaine d.