The Continuum Limit of a Fermion System Involving Leptons and Quarks:   Strong, Electroweak and Gravitational Interactions
  The causal action principle is analyzed for a system of relativistic fermions composed of massive Dirac particles and neutrinos. In the continuum limit, we obtain an effective interaction described by classical gravity as well as the strong and electroweak gauge fields of the standard model. 
Felix Finster
math-ph gr-qc hep-th math.MP