Time evolution in a geometric model of a particle
  We analyse the properties of a (4+1)-dimensional Ricci-flat spacetime which may be viewed as an evolving Taub-NUT geometry, and give exact solutions of the Maxwell and gauged Dirac equation on this background. We interpret these solutions in terms of a geometric model of the electron and its spin, and discuss links between the resulting picture and Dirac's Large Number Hypothesis. 
Michael Atiyah, Guido Franchetti and Bernd Schroers
hep-th gr-qc math-ph math.MP