Supersymmetric Composite Models on Intersecting D-branes
  We construct supersymmetric composite models of quarks and leptons from type IIA T^6/(Z_2 x Z_2) orientifolds with intersecting D6-branes. In case of T^6 = T^2 x T^2 x T^2 with no tilted T^2, a composite model of the supersymmetric SU(5) grand unified theory with three generations is constructed. In case of that one T^2 is tilted, a composite model with SU(3)_c x SU(2)_L x U(1)_Y gauge symmetry with three generations is constructed. These models are not realistic, but contain fewer additional exotic particles and U(1) gauge symmetries due to the introduction of the compositeness of quarks and leptons. The masses of some exotic particles are naturally generated through the Yukawa interactions among "preons". 
Noriaki Kitazawa