Higgs and Fermions in D4-D5-E6 Model based on Cl(0,8) Clifford Algebra
  This paper discusses the Higgs and spinor fermion terms of the D4-D5-E6 model of a series of papers (hep-ph/9301210, hep-th/9302030, hep-th/9306011, and hep-th/9402003) an 8-dimensional spacetime is reduced to 4-dimensions. The gauge boson terms give SU(3)xSU(2)xU(1) for the color, weak, and electromagnetic forces and gravity of the MacDowell-Mansouri type, which has recently been shown by Nieto, Obregon, and Socorro (gr-qc/9402029) to be equivalent, up to a Pontrjagin topological term, to the Ashtekar formulation. 
F. D. T. Smith