On the Particle Interpretation for the Quantized Fields in External Field Problems

Abstract

We review the main recent results concerning the capacity of the quantized field system in the presence of an external field to represent physical particles at all times. We deal more particularly with the Dirac spin 1/2 equation since it is known to be trouble free at the c number level. As this had not been done explicitly before, we present a proof, valid for a wide class of potentials, which shows that at each time a Fock basis for individual energy quanta (the physical particles) exists in the same Hilbert space, i.e. the system can be completely described in terms of these.