Weak Mixing Angle and the SU(3)_C times SU(3) Model on M^4 times   S^1/(Z_2 times Z_2')
  We show that the desirable weak mixing angle sin^2 theta_W = 0.2312 at m_Z scale can be generated naturally in the SU(3)_C times SU(3) model on M^4 times S^1 / (Z_2 times Z_2') where the gauge symmetry SU(3) is broken down to SU(2)_L times U(1)_Y by orbifold projection. For a supersymmetric model with a TeV scale extra dimension, the SU(3) unification scale is about hundreds of TeVs at which the gauge couplings for SU(3)_C and SU(3) can also be equal in the mean time. For the non-supersymmetric model, SU(2)_L times U(1)_Y are unified at order of 10 TeV. These models may serve as good candidates for physics beyond the SM or MSSM. 
Tianjun Li, Liao Wei