Electroweak unification of quarks and leptons in a gauge group   $SU_{C}(3)\times SU(4)\times U_{X}(1)$
  A model for electroweak unification of quarks and leptons, in a gauge group $SU_{C}(3)\times SU(4)\times U_{X}(1)$ is constructed. The model requires, three generations of quarks and leptons which are replicas (mirror) of the standard quarks and leptons. The gauge group $SU(4)\times U_{X}(1)$ is broken in such a way so as to reproduce standard model and to generate heavy masses for the vector bosons ($W^{\pm}_{R_{\mu}}$, $Z^{\prime}_{\mu}$,$Z^{\prime\prime}_{\mu}$), the leptoquarks and mirror fermions. It is shown lower limit on mass scale of mirror fermions is $m_{E}\geq\frac{m_{Z}}{2}$, $E^{-}$ being the lightest mirror fermion coupled to Z boson. As the universe expands, the heavy matter is decoupled at an early stage of expansion and may be a source of dark matter. Leptoquarks in the model connect the standard model and mirror fermions. Baryon genesis in our Universe implies antibaryon genesis in mirror Universe. 
Fayyazuddin
hep-ph