About Zitterbewegung and electron structure
  We start from the spinning electron theory by Barut and Zanghi, which has been recently translated into the Clifford algebra language. We "complete" such a translation, first of all, by expressing in the Clifford formalism a particular Barut-Zanghi (BZ) solution, which refers (at the classical limit) to an internal helical motion with a time-like speed [and is here shown to originate from the superposition of positive and negative frequency solutions of the Dirac equation]. Then, we show how to construct solutions of the Dirac equation describing helical motions with light-like speed, which meet very well the standard interpretation of the velocity operator in the Dirac equation theory (and agree with the solution proposed by Hestenes, on the basis --however-- of ad-hoc assumptions that are unnecessary in the present approach). The above results appear to support the conjecture that the Zitterbewegung motion (a helical motion, at the classical limit) is responsible for the electron spin. 
W.A.Rodrigues Jr., Jayme Vaz, Erasmo Recami and G.Salesi