The barut and zanghi model, and some generalizations

In this paper we give a detailed analysis of the Barut and Zanghi (BZ) model, which can be seen as a classical model for a Dirac particle. We show that all helical worldlines in the BZ model have vanishing third curvature. We also study some generalizations of the BZ model. There is a particularly interesting one, considered in detail, which can be seen as a classical model for Heisenberg program of a unified field theory of elementary particles.