On the gauge coupling unification

We consider a quark-lepton symmetry model of unification of the strong and electromagnetic interactions. The model has the gauge group $SU(4)\times U(1)_{Y}$ and the minimal Higgs structure consisting of one complex quartet of scalar particles. The spontaneous breakdown of the gauge group to $SU(3)_{c}\times U(1)_{em}$ due to nonzero vacuum expectation value of the Higgs quartet provides the simplest realization of the Higgs mechanism which generates masses for gauge bosons, and masses to quarks and leptons. Using the embedding of the gauge group to SU(5), we study the evolution of coupling constants and find a connection of the couplings with the gauge couplings of the standard model.