Supersymmetric Pati-Salam Models from Intersecting D6-branes: A Road to   the Standard Model
  We provide a systematic construction of three-family N=1 supersymmetric Pati-Salam models from Type IIA orientifolds on $\IT^6/(\IZ_2\times \IZ_2)$ with intersecting D6-branes. All the gauge symmetry factors $SU(4)_C\times SU(2)_L \times SU(2)_R$ arise from the stacks of D6-branes with U(n) gauge symmetries, while the ``hidden sector'' is specified by $USp(n)$ branes, parallel with the orientifold planes or their ${\bf Z_2}$ images. The Pati-Salam gauge symmetry can be broken down to the $SU(3)_C\times SU(2)_L\times U(1)_{B-L} \times U(1)_{I_{3R}}$ via D6-brane splittings, and further down to the Standard Model via D- and F-flatness preserving Higgs mechanism from massless open string states in a N=2 subsector. The models also possess at least two confining hidden gauge sectors, where gaugino condensation can in turn trigger supersymmetry breaking and (some) moduli stabilization. The systematic search yields 11 inequivalent models: 8 models with less than 9 Standard model Higgs doublet-pairs and 1 model with only 2 Standard Model Higgs doublet-pairs, 2 models possess at the string scale the gauge coupling unification of $SU(2)_L$ and $SU(2)_R$, and all the models possess additional exotic matters. We also make preliminary comments on phenomenological implications of these models. 
Mirjam Cvetic, Tianjun Li, Tao Liu